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Western blot

The western blot (sometimes called the protein immunoblot), or western blotting, is a widely used analytical technique in molecular biology and immunogenetics to detect specific proteins in a sample of tissue homogenate or extract. Besides detecting the proteins, this technique is also utilized to visualize, distinguish, and quantify the different proteins in a complicated protein combination.

Western blot technique uses three elements to achieve its task of separating a specific protein from a complex: separation by size, transfer of protein to a solid support, and marking target protein using a primary and secondary antibody to visualize. A synthetic or animal-derived antibody (known as the primary antibody) is created that recognizes and binds to a specific target protein. The electrophoresis membrane is washed in a solution containing the primary antibody, before excess antibody is washed off. A secondary antibody is added which recognizes and binds to the primary antibody. The secondary antibody is visualized through various methods such as staining, immunofluorescence, and radioactivity, allowing indirect detection of the specific target protein.

Other related techniques include dot blot analysis, quantitative dot blot, immunohistochemistry and immunocytochemistry, where antibodies are used to detect proteins in tissues and cells by immunostaining, and enzyme-linked immunosorbent assay (ELISA).

The name western blot is a play on the Southern blot, a technique for DNA detection named after its inventor, English biologist Edwin Southern. Similarly, detection of RNA is termed as northern blot. The term "western blot" was given by W. Neal Burnette in 1981, although the method itself was independently invented in 1979 by Jaime Renart, Jakob Reiser, and George Stark at Stanford University, and by Harry Towbin, Theophil Staehelin, and Julian Gordon at the Friedrich Miescher Institute in Basel, Switzerland. The Towbin group also used secondary antibodies for detection, thus resembling the actual method that is almost universally used today. Between 1979 and 2019 "it has been mentioned in the titles, abstracts, and keywords of more than 400,000 PubMed-listed publications" and may still be the most used protein-analytical technique.

Applications
The western blot is extensively used in biochemistry for the qualitative detection of single proteins and protein-modifications (such as post-translational modifications). At least 8–9% of all protein-related publications are estimated to apply western blots. It is used as a general method to identify the presence of a specific single protein within a complex mixture of proteins. A semi-quantitative estimation of a protein can be derived from the size and colour intensity of a protein band on the blot membrane. In addition, applying a dilution series of a purified protein of known concentrations can be used to allow a more precise estimate of protein concentration. The western blot is routinely used for verification of protein production after cloning. It is also used in medical diagnostics, e.g., in the HIV test or BSE-Test.

The confirmatory HIV test employs a western blot to detect anti-HIV antibody in a human serum sample. Proteins from known HIV-infected cells are separated and blotted on a membrane as above. Then, the serum to be tested is applied in the primary antibody incubation step; free antibody is washed away, and a secondary anti-human antibody linked to an enzyme signal is added. The stained bands then indicate the proteins to which the patient's serum contains antibody. A western blot is also used as the definitive test for variant Creutzfeldt–Jakob disease, a type of prion disease linked to the consumption of contaminated beef from cattle with bovine spongiform encephalopathy (BSE, commonly referred to as 'mad cow disease'). Another application is in the diagnosis of tularemia. An evaluation of the western blot's ability to detect antibodies against F. tularensis revealed that its sensitivity is almost 100% and the specificity is 99.6%. Some forms of Lyme disease testing employ western blotting. A western blot can also be used as a confirmatory test for Hepatitis B infection and HSV-2 (Herpes Type 2) infection. In veterinary medicine, a western blot is sometimes used to confirm FIV+ status in cats.

Further applications of the western blot technique include its use by the World Anti-Doping Agency (WADA). Blood doping is the misuse of certain techniques and/or substances to increase one's red blood cell mass, which allows the body to transport more oxygen to muscles and therefore increase stamina and performance. There are three widely known substances or methods used for blood doping, namely, erythropoietin (EPO), synthetic oxygen carriers and blood transfusions. Each is prohibited under WADA's List of Prohibited Substances and Methods. The western blot technique was used during the 2014 FIFA World Cup in the anti-doping campaign for that event. In total, over 1000 samples were collected and analysed by Reichel, et al. in the WADA accredited Laboratory of Lausanne, Switzerland. Recent research utilizing the western blot technique showed an improved detection of EPO in blood and urine based on novel Velum SAR precast horizontal gels optimized for routine analysis. With the adoption of the horizontal SAR-PAGE in combination with the precast film-supported Velum SAR gels the discriminatory capacity of micro-dose application of rEPO was significantly enhanced.

In addition to the application of western blot in scientific research, it is also utilized in clinical research areas. Since it can be applied to the direct protein identification process, western blot is regarded as a powerful diagnostic tool that is frequently used in the clinic setting. WB and protein detection techniques can be used to find disease biomarkers like specific proteins or antibodies. It is thought to be a viable method for identifying particular proteins during the diagnosis of diseases like cancer, autoimmune disease, and prion disorders. The detection of several biomarkers used in the diagnosis of neurological and oncological illnesses by Western blotting is a common procedure. For instance, it is widely believed that the advent of multidrug resistance (MDR) has made effective cancer therapy extremely challenging. Therefore, early, accurate, and sensitive MDR mechanism discovery is essential, as is the search for more effective chemotherapeutic approaches for application in clinical settings. The expression of MDR1/P-glycoprotein in the P388/ADR, P388 and HCT-15 cell lines is examined using the WB technique. WB has also identified MRP1 levels.

On the other hand, as western blot has the potential to distinguish different protein isoforms, it may be used to diagnose prion and protein isoform-related diseases, such as cancer. For instance, the western blotting analysis of the isoform pattern of 14-3-3 proteins in cerebral fluid can identify Creutzfeldt-Jakob disease. Also, Farmers lung disease is a pulmonary condition brought on by breathing antigenic particles, and studies have indicated that western blot may be a useful option for identifying immunoreactive proteins related to farmers lung disease. Besides, western blot is also used to identify proteins in synovial fluid and serum, enabling the diagnosis of osteoarthritis and rheumatoid arthritis clinical symptoms. western blot is used to assess the levels of FSTL1 protein expression in individuals with knee osteoarthritis, which serves as a potential biomarker of articular damage. Additionally, it is used to identify proteins in synovial fluid and serum, enabling the diagnosis of osteoarthritis and rheumatoid arthritis clinical symptoms. It is used to assess the levels of FSTL1 protein expression in individuals with knee osteoarthritis, which serves as a potential biomarker of articular damage.

Identification of protein localization across cells
For medication development, the identification of therapeutic targets, and biological research, it is essential to comprehend where proteins are located within a cell. The subcellular locations of proteins inside the cell and their functions are closely related. The relationship between protein function and localization suggests that when proteins move, their functions may change or acquire new characteristics. A protein's subcellular placement can be determined using a variety of methods. Numerous efficient and reliable computational tools and strategies have been created and used to identify protein subcellular localization. With the aid of subcellular fractionation methods, WB continues to be an important fundamental method for the investigation and comprehension of protein localization.

Epitope mapping
Due to their various epitopes, antibodies have gained interest in both basic and clinical research. The foundation of antibody characterization and validation is epitope mapping. The procedure of identifying an antibody's binding sites (epitopes) on the target protein is referred to as "epitope mapping." Finding the binding epitope of an antibody is essential for the discovery and creation of novel vaccines, diagnostics, and therapeutics. As a result, various methods for mapping antibody epitopes have been created. At this point, western blotting's specificity is the main feature that sets it apart from other epitope mapping techniques. There are several application of western blot for epitope mapping on human skin samples, hemorrhagic disease virus.

Procedure
The western blot method is composed of gel electrophoresis to separate native proteins by 3-D structure or denatured proteins by the length of the polypeptide, followed by an electrophoretic transfer onto a membrane (mostly PVDF or nitrocellulose) and an immunostaining procedure to visualize a certain protein on the blot membrane.

Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) is generally used for the denaturing electrophoretic separation of proteins. Sodium dodecyl sulfate (SDS) is generally used as a buffer (as well as in the gel) in order to give all proteins present a uniform negative charge, since proteins can be positively, negatively, or neutrally charged. Prior to electrophoresis, protein samples are often boiled to denature the proteins present. This ensures that proteins are separated based on size and prevents proteases (enzymes that break down proteins) from degrading samples. Following electrophoretic separation, the proteins are transferred to a membrane (typically nitrocellulose or PVDF). The membrane is often then stained with Ponceau S in order to visualize the proteins on the blot and ensure a proper transfer occurred. Next the proteins are blocked with milk (or other blocking agents) to prevent non-specific antibody binding, and then stained with antibodies specific to the target protein. Lastly, the membrane will be stained with a secondary antibody that recognizes the first antibody staining, which can then be used for detection by a variety of methods. The gel electrophoresis step is included in western blot analysis to resolve the issue of the cross-reactivity of antibodies.

Sample Preparation
As a significant step in conducting a western blot, sample preparation has to be done effectively since the interpretation of this assay is influenced by the protein preparation, which is composed of protein extraction and purification processes. To achieve efficient protein extraction, a proper homogenization method needs to be chosen due to the fact that it is responsible for bursting the cell membrane and releasing the intracellular components. Besides that, the ideal lysis buffer is needed to acquire substantial amounts of target protein content because the buffer is leading the process of protein solubilization and preventing protein degradation. After completing the sample preparation, the protein content is ready to be separated by the utilization of gel electrophoresis.

Gel electrophoresis
The proteins of the sample are separated using gel electrophoresis. Separation of proteins may be by isoelectric point (pI), molecular weight, electric charge, or a combination of these factors. The nature of the separation depends on the treatment of the sample and the nature of the gel.

By far the most common type of gel electrophoresis employs polyacrylamide gels and buffers loaded with sodium dodecyl sulfate (SDS). SDS-PAGE (SDS-polyacrylamide gel electrophoresis) maintains polypeptides in a denatured state once they have been treated with strong reducing agents to remove secondary and tertiary structure (e.g. disulfide bonds [S-S] to sulfhydryl groups [SH and SH]) and thus allows separation of proteins by their molecular mass. Sampled proteins become covered in the negatively charged SDS, effectively becoming anionic, and migrate towards the positively charged (higher voltage) anode (usually having a red wire) through the acrylamide mesh of the gel. Smaller proteins migrate faster through this mesh, and the proteins are thus separated according to size (usually measured in kilodaltons, kDa). The concentration of acrylamide determines the resolution of the gel – the greater the acrylamide concentration, the better the resolution of lower molecular weight proteins. The lower the acrylamide concentration, the better the resolution of higher molecular weight proteins. Proteins travel only in one dimension along the gel for most blots.

Samples are loaded into wells in the gel. One lane is usually reserved for a marker or ladder, which is a commercially available mixture of proteins of known molecular weights, typically stained so as to form visible, coloured bands. When voltage is applied along the gel, proteins migrate through it at different speeds dependent on their size. These different rates of advancement (different electrophoretic mobilities) separate into bands within each lane. Protein bands can then be compared to the ladder bands, allowing estimation of the protein's molecular weight.

It is also possible to use a two-dimensional gel which spreads the proteins from a single sample out in two dimensions. Proteins are separated according to isoelectric point (pH at which they have a neutral net charge) in the first dimension, and according to their molecular weight in the second dimension.

Transfer
To make the proteins accessible to antibody detection, they are moved from within the gel onto a membrane, a solid support, which is an essential part of the process. There are two types of membrane: nitrocellulose (NC) or polyvinylidene difluoride (PVDF). NC membrane has high affinity for protein and its retention abilities. However, NC is brittle, and does not allow the blot to be used for re-probing, whereas PVDF membrane allows the blot to be re-probed. The most commonly used method for transferring the proteins is called electroblotting. Electroblotting uses an electric current to pull the negatively charged proteins from the gel towards the positively charged anode, and into the PVDF or NC membrane. The proteins move from within the gel onto the membrane while maintaining the organization they had within the gel. An older method of transfer involves placing a membrane on top of the gel, and a stack of filter papers on top of that. The entire stack is placed in a buffer solution which moves up the paper by capillary action, bringing the proteins with it. In practice this method is not commonly used due to the lengthy procedure time.

As a result of either transfer process, the proteins are exposed on a thin membrane layer for detection. Both varieties of membrane are chosen for their non-specific protein binding properties (i.e. binds all proteins equally well). Protein binding is based upon hydrophobic interactions, as well as charged interactions between the membrane and protein. Nitrocellulose membranes are cheaper than PVDF, but are far more fragile and cannot withstand repeated probings.

Total protein staining
Total protein staining allows the total protein that has been successfully transferred to the membrane to be visualised, allowing the user to check the uniformity of protein transfer and to perform subsequent normalization of the target protein with the actual protein amount per lane. Normalization with the so-called "loading control" was based on immunostaining of housekeeping proteins in the classical procedure, but is heading toward total protein staining recently, due to multiple benefits. At least seven different approaches for total protein staining have been described for western blot normalization: Ponceau S, stain-free techniques, Sypro Ruby, Epicocconone, Coomassie R-350, Amido Black, and Cy5. In order to avoid noise of signal, total protein staining should be performed before blocking of the membrane. Nevertheless, post-antibody stainings have been described as well.

Blocking
Since the membrane has been chosen for its ability to bind protein and as both antibodies and the target are proteins, steps must be taken to prevent the interactions between the membrane and the antibody used for detection of the target protein. Blocking of non-specific binding is achieved by placing the membrane in a dilute solution of protein – typically 3–5% bovine serum albumin (BSA) or non-fat dry milk (both are inexpensive) in tris-buffered saline (TBS) or I-Block, with a minute percentage (0.1%) of detergent such as Tween 20 or Triton X-100. Although non-fat dry milk is preferred due to its availability, an appropriate blocking solution is needed as not all proteins in milk are compatible with all the detection bands. The protein in the dilute solution attaches to the membrane in all places where the target proteins have not attached. Thus, when the antibody is added, it cannot bind to the membrane, and therefore the only available binding site is the specific target protein. This reduces background in the final product of the western blot, leading to clearer results, and eliminates false positives.

Incubation
During the detection process, the membrane is "probed" for the protein of interest with a modified antibody which is linked to a reporter enzyme; when exposed to an appropriate substrate, this enzyme drives a colorimetric reaction and produces a colour. For a variety of reasons, this traditionally takes place in a two-step process, although there are now one-step detection methods available for certain applications.

Primary antibody
The primary antibodies are generated when a host species or immune cell culture is exposed to the protein of interest (or a part thereof). Normally, this is part of the immune response, whereas here they are harvested and used as sensitive and specific detection tools that bind the protein directly.

After blocking, a solution of primary antibody (generally between 0.5 and 5 micrograms/mL) diluted in either PBS or TBST wash buffer is incubated with the membrane under gentle agitation for typically an hour at room temperature, or overnight at 4°C. It can also be incubated at different temperatures, with lesser temperatures being associated with more binding, both specific (to the target protein, the "signal") and non-specific ("noise"). Following incubation, the membrane is washed several times in wash buffer to remove unbound primary antibody, and thereby minimize background. Typically, the wash buffer solution is composed of buffered saline solution with a small percentage of detergent, and sometimes with powdered milk or BSA.

Secondary antibody
After rinsing the membrane to remove unbound primary antibody, the membrane is exposed to another antibody known as the secondary antibody. Antibodies come from animal sources (or animal sourced hybridoma cultures). The secondary antibody recognises and binds to the species-specific portion of the primary antibody. Therefore, an anti-mouse secondary antibody will bind to almost any mouse-sourced primary antibody, and can be referred to as an 'anti-species' antibody (e.g. anti-mouse, anti-goat etc.). To allow detection of the target protein, the secondary antibody is commonly linked to biotin or a reporter enzyme such as alkaline phosphatase or horseradish peroxidase. This means that several secondary antibodies will bind to one primary antibody and enhance the signal, allowing the detection of proteins of a much lower concentration than would be visible by SDS-PAGE alone.

Horseradish peroxidase is commonly linked to secondary antibodies to allow the detection of the target protein by chemiluminescence. The chemiluminescent substrate is cleaved by horseradish peroxidase, resulting in the production of luminescence. Therefore, the production of luminescence is proportional to the amount of horseradish peroxidase-conjugated secondary antibody, and therefore, indirectly measures the presence of the target protein. A sensitive sheet of photographic film is placed against the membrane, and exposure to the light from the reaction creates an image of the antibodies bound to the blot. A cheaper but less sensitive approach utilizes a 4-chloronaphthol stain with 1% hydrogen peroxide; the reaction of peroxide radicals with 4-chloronaphthol produces a dark purple stain that can be photographed without using specialized photographic film.

As with the ELISPOT and ELISA procedures, the enzyme can be provided with a substrate molecule that will be converted by the enzyme to a coloured reaction product that will be visible on the membrane (see the figure below with blue bands).

Another method of secondary antibody detection utilizes a near-infrared fluorophore-linked antibody. The light produced from the excitation of a fluorescent dye is static, making fluorescent detection a more precise and accurate measure of the difference in the signal produced by labeled antibodies bound to proteins on a western blot. Proteins can be accurately quantified because the signal generated by the different amounts of proteins on the membranes is measured in a static state, as compared to chemiluminescence, in which light is measured in a dynamic state.

A third alternative is to use a radioactive label rather than an enzyme coupled to the secondary antibody, such as labeling an antibody-binding protein like Staphylococcus Protein A or Streptavidin with a radioactive isotope of iodine. Since other methods are safer, quicker, and cheaper, this method is now rarely used; however, an advantage of this approach is the sensitivity of auto-radiography-based imaging, which enables highly accurate protein quantification when combined with optical software (e.g. Optiquant).

One step
Historically, the probing process was performed in two steps because of the relative ease of producing primary and secondary antibodies in separate processes. This gives researchers and corporations huge advantages in terms of flexibility, reduction of cost, and adds an amplification step to the detection process. Given the advent of high-throughput protein analysis and lower limits of detection, however, there has been interest in developing one-step probing systems that would allow the process to occur faster and with fewer consumables. This requires a probe antibody which both recognizes the protein of interest and contains a detectable label, probes which are often available for known protein tags. The primary probe is incubated with the membrane in a manner similar to that for the primary antibody in a two-step process, and then is ready for direct detection after a series of wash steps.

Detection and visualization
After the unbound probes are washed away, the western blot is ready for detection of the probes that are labeled and bound to the protein of interest. In practical terms, not all westerns reveal protein only at one band in a membrane. Size approximations are taken by comparing the stained bands to that of the marker or ladder loaded during electrophoresis. The process is commonly repeated for a structural protein, such as actin or tubulin, that should not change between samples. The amount of target protein is normalized to the structural protein to control between groups. A superior strategy is the normalization to the total protein visualized with trichloroethanol or epicocconone. This practice ensures correction for the amount of total protein on the membrane in case of errors or incomplete transfers. (see western blot normalization)

Colorimetric detection
The colorimetric detection method depends on incubation of the western blot with a substrate that reacts with the reporter enzyme (such as peroxidase) that is bound to the secondary antibody. This converts the soluble dye into an insoluble form of a different colour that precipitates next to the enzyme and thereby stains the membrane. Development of the blot is then stopped by washing away the soluble dye. Protein levels are evaluated through densitometry (how intense the stain is) or spectrophotometry.

Chemiluminescent detection
Chemiluminescent detection methods depend on incubation of the western blot with a substrate that will luminesce when exposed to the reporter on the secondary antibody. The light is then detected by CCD cameras which capture a digital image of the western blot or photographic film. The use of film for western blot detection is slowly disappearing because of non linearity of the image (non accurate quantification). The image is analysed by densitometry, which evaluates the relative amount of protein staining and quantifies the results in terms of optical density. Newer software allows further data analysis such as molecular weight analysis if appropriate standards are used.

Radioactive detection
Radioactive labels do not require enzyme substrates, but rather, allow the placement of medical X-ray film directly against the western blot, which develops as it is exposed to the label and creates dark regions which correspond to the protein bands of interest (see image above). The importance of radioactive detections methods is declining due to its hazardous radiation, because it is very expensive, health and safety risks are high, and ECL (enhanced chemiluminescence) provides a useful alternative.

Fluorescent detection
The fluorescently labeled probe is excited by light and the emission of the excitation is then detected by a photosensor such as a CCD camera equipped with appropriate emission filters which captures a digital image of the western blot and allows further data analysis such as molecular weight analysis and a quantitative western blot analysis. Fluorescence is considered to be one of the best methods for quantification but is less sensitive than chemiluminescence.

Secondary probing
One major difference between nitrocellulose and PVDF membranes relates to the ability of each to support "stripping" antibodies off and reusing the membrane for subsequent antibody probes. While there are well-established protocols available for stripping nitrocellulose membranes, the sturdier PVDF allows for easier stripping, and for more reuse before background noise limits experiments. Another difference is that, unlike nitrocellulose, PVDF must be soaked in 95% ethanol, isopropanol or methanol before use. PVDF membranes also tend to be thicker and more resistant to damage during use.

Minimum requirement specification for Western Blot
In order to ensure that the results of Western blots are reproducible, it is important to report the various parameters mentioned above, including specimen preparation, the concentration of protein used for loading, the percentage of gel and running condition, various transfer methods, attempting to block conditions, the concentration of antibodies, and identification and quantitative determination methods. Many of the articles that have been published don't cover all of these variables. Hence, it is crucial to describe different experimental circumstances or parameters in order to increase the repeatability and precision of WB. To increase WB repeatability, a minimum reporting criteria is thus required.

2-D gel electrophoresis
Two-dimensional SDS-PAGE uses the principles and techniques outlined above. 2-D SDS-PAGE, as the name suggests, involves the migration of polypeptides in 2 dimensions. For example, in the first dimension, polypeptides are separated according to isoelectric point, while in the second dimension, polypeptides are separated according to their molecular weight. The isoelectric point of a given protein is determined by the relative number of positively (e.g. lysine, arginine) and negatively (e.g. glutamate, aspartate) charged amino acids, with negatively charged amino acids contributing to a low isoelectric point and positively charged amino acids contributing to a high isoelectric point. Samples could also be separated first under nonreducing conditions using SDS-PAGE, and under reducing conditions in the second dimension, which breaks apart disulfide bonds that hold subunits together. SDS-PAGE might also be coupled with urea-PAGE for a 2-dimensional gel.

In principle, this method allows for the separation of all cellular proteins on a single large gel. A major advantage of this method is that it often distinguishes between different isoforms of a particular protein – e.g. a protein that has been phosphorylated (by addition of a negatively charged group). Proteins that have been separated can be cut out of the gel and then analysed by mass spectrometry, which identifies their molecular weight.

Detection problems
There may be a weak or absent signal in the band for a number of reasons related to the amount of antibody and antigen used. This problem might be resolved by using the ideal antigen and antibody concentrations and dilutions specified in the supplier's data sheet. Increasing the exposition period in the detection system's software can address weak bands caused by lower sample and antibody concentrations.

Multiple band problems
When the protein is broken down by proteases, several bands other than predicted bands of low molecular weight might appear. The development of numerous bands can be prevented by properly preparing protein samples with enough protease inhibitors. Multiple bands might show up in the high molecular weight region because some proteins form dimers, trimers, and multimers; this issue might be solved by heating the sample for longer periods of time. Proteins with post-translational modifications (PTMs) or numerous isoforms cause several bands to appear at various molecular weight areas. PTMs can be removed from a specimen using specific chemicals, which also remove extra bands.

High background
Strong antibody concentrations, inadequate blocking, inadequate washing, and excessive exposure time during imaging can result in a high background in the blots. A high background in the blots could be avoided by fixing these issues.

Irregular and uneven bands
It has been claimed that a variety of odd and unequal bands, including black dots, white spots or bands, and curving bands, have occurred. The block dots are removed from the blots by effective blocking. White patches develop as a result of bubbles between the membrane and gel. White bands appear in the blots when main and secondary antibodies are present in significant concentrations. Because of the high voltage used during the gel run and the rapid protein migration, smiley bands appear in the blots. The strange bands in the blot are resolved by resolving these problems.

Improvements for Western Blot Related Problems
During the western blotting, there could be several problems related to the different steps of this procedure. Those problems could originate from a protein analysis step such as the detection of low- or post-translationally modified proteins. Additionally, they can be based on the selection of antibodies since the quality of the antibodies plays a significant role in the detection of proteins specifically. On account of the presence of these kinds of problems, a variety of improvements are being produced in the fields of preparation of cell lysate and blotting procedures to build up reliable results. Moreover, to achieve more sensitive analysis and overcome the problems associated with western blotting, several different techniques have been developed and utilized, such as far-western blotting, diffusion blotting, single-cell resolution western blotting, and automated microfluidic western blotting.

Presentation
Researchers use different software to process and align image-sections for elegant presentation of western blot results. Popular tools include Sciugo, Microsoft PowerPoint, Adobe Illustrator and GIMP.

Enhanced Western Blot
Since 1980, western blot has emerged as the most used method in molecular biology for determining the presence and quantity of a certain protein. Over the years, plenty of "advanced" and "optimized" systematical methods have been developed. These developments provide advanced and more sensitive results, with the aid of more advanced imaging technologies and modern fluorescent labeling methods.

Shift-western blot
The method with the highest adoption rate for determining DNA-binding proteins and protein-DNA interactions is the electrophoretic mobility shift test. Protein-DNA complexes are analysed via shift-WB. It is created by transferring protein-DNA complexes, in which the DNA in the charged membrane is positioned beneath the nitrocellulose membrane while the proteins are kept in the membrane. Then, specific antibodies are used to identify the proteins, and a radioactive label is used to identify the DNA. Furthermore, the transmitted proteins and DNA can be retrieved and examined in greater detail.

Single-cell western blot
The single-cell WB (scWB), in addition to the conventional WB, is regarded as a breakthrough in the study of protein subcellular localization and in the evaluation of single-cell protein. When measuring the levels and conditions of protein expression from one cell to the next, it is used. With the aid of single-cell WB, the western blot's selectivity and specificity were expanded to include single-cell protein analysis. The limitations of antibody accuracy and sensitivity are overcome by this technique. Furthermore, because of its versatility, it may be utilized to measure numerous target proteins concurrently from different cell lines and single cells.

Quantifiable fluorescence-based western blot
The development known as quantifiable fluorescence-based WB (QFWB) enables researchers to carry out comparative expression analysis with better sensitivity and precision than ever before. Quantifiable in QFWB refers to genuinely quantitative with increased sensitivity. This method is employed to identify the minute expression variations between various samples. With the aid of a secondary antibody that has been fluorescently tagged, QFWB produces a linear detection profile. Modern QFWB techniques enable simultaneous dual labeling and are more sensitive to identify minute variations.

Quantitative computerized western blot
Quantitative computerized western blot analyses the reactivity of individual antibodies to specific antigens to identify immunodominant and immunorecessive determinants using two measures, such as net band intensity and total lane intensity of the WB. The creation of quick serodiagnostic tests and efficient vaccines is made possible by the identification of certain immunodominant antigens.The study looks for serological markers for the early diagnosis of cancer, viral, and autoimmune illnesses using quantitative computerized western blot.

High-throughput western blot (DigiWest)
It is a technique that combines conventional SDS-PAGE protein resolution with a bead-based microarray platform that immobilizes proteins on microspheres. This combination of protein separation, uniformity, and sensitivity allows for the quick quantification of a number of different protein targets as well as their changes. The benefit of DigiWest is that western blot is carried out using beads-based microarrays, allowing for the simultaneous detection and analysis of hundreds of distinct proteins and their changes using a wide range of varied antibodies.

Microfluidic western blot
In order to detect many proteins on a single microfluidic chip, microfluidic western blot is carried out using a number of processes, including sample enrichment, protein size, deposition of protein, and then in situ antibody probing. A photoreactive (UV light) polyacrylamide gel and a photopatternable (blue-light) surface are the foundation of this multistep procedure. Due to improvements in analytical performance, WB may now be completed in 10–60 minutes while maintaining high sensitivity detection limits (50 picomoles) and multiplexed component detection levels (femtograms). Therefore, by fusing superb specificity and the high-throughput benefits of multiplexing, WB creates a cornerstone for quick proteomics.

Multistrip western blot
A enhanced WB technique called multistrip WB is based on the simultaneous transfer of different proteins from a number of polyacrylamide gel strips to a single polyvinylidene difluoride or nitrocellulose membrane. Multistrip WB allows for the simultaneous monitoring of up to nine separate proteins from the same loading of the sample and up to a tenfold increase in data output for a single WB cycle. Systems biology, cell signaling research, and biomedical diagnostics would all benefit from using this technique.

Microchip capillary electrophoresis-based western blot
The capillary and microchip electrophoresis-based western blot was created to reduce the quantity of protein samples and the amount of time it takes to execute western blot. It contributes to the more sensitive and accurate measurement of various protein targets from any single-cell lysate carried out on a microchip. 400 nanograms of cell lysate are all that is needed to identify and quantify eleven different proteins.

title: Western blot


text:
Talk:Self-organizing map

Old comments
Looks interesting, but this is not a place for academics to promote concepts not widely discussed - somewhere other than their own pet web site. Please outline what an SOM actually is, with examples, so that this can be a proper article. —The preceding unsigned comment was added by Special:Contributions/ (talk)

 * Agreed, it still needs some explaination. But please, the entry was already there (I did not start a new item), and I think I added quite some good links (not my own 'pet-web' by the way). Are you anti-academic? Pieter Suurmond 00:25 Jan 25, 2003 (UTC)

 * Yes, I am anti-academic. So what?  The rules are the rules, and the idea must be explained here fully.  So, for instance, you must explain exactly what you mean by wikipedia being "an example of" this paradigm.  If you mean it is an example of self-organizing systems, then that belongs in that article, not in this article about something more specific. —The preceding unsigned comment was added by Special:Contributions/ (talk)

 * Kohonen Maps are far from being a 'concept not widely disscussed' : international conferences about data analysis and neural networks almost always have special sessions dedicated to it. It also has its own bi-annual international conference : WSOM held in Japan two years ago and in France this year. Nevertheless, the article needs a lot of work to present the SOM adequately. [df] —The preceding unsigned comment was added by Special:Contributions/ (talk)

 * "...and several thousand scientific articles have been written about it." - The fact that an anti-academic on wikipedia is unfamiliar with Kohonen Maps and calls them something "not widely discussed" probably doesn't justify this clause. It adds no more useful information than mentioning "several thousand journal articles have been written about the concept" would add to the Riemannian manifold page, for example. A mention of a few key articles or applications would be more informative. Geo.per 19:01, 26 June 2006 (UTC)

 Easy guys, name calling won't get you nowhere Paskari 21:38, 1 December 2006 (UTC)

I just wanted to add, that SOM are impotant to have even if the article is not perfect yet. Because the history of the self-organizing map goes a while back, i would suggest the introduction of some historical references, as well as some review articles. --MNegrello (talk) 01:02, 16 September 2008 (UTC)

JPEG upload problems?
Something went wrong with the 3 .jpg files I uploaded.... They don't seem to load...

Reference space and data space (codebook vectors)
Perhaps it should be stressed that the neighbourhood is defined by means of a reference space (the map) as opposed to the data space, which specifies the winning neuron by distance to its corresponding codebook vector. —The preceding unsigned comment was added by Special:Contributions/ (talk)

desired outputs?
I deleted following sentence: "Unsupervised learning" is, technically, supervised in that we do have a desired output.

It doesn't make sense, what is the "desired output"?

Update: Now I think I understand that this probably refers to the fact that weights are moved towards the input vector. I still don't think this justifies calling SOM supervised, because there is no a priori desired output value for an input. AnAj 15:39, 18 June 2006 (UTC)

Subset Issue
The first line reads "The self-organizing map (SOM) is a subtype of artificial neural networks", that's like me saying "a toyota is a subtype of automobile". Can we clear this up please Paskari 21:38, 1 December 2006 (UTC)

Some Variables Issue
In the Some variables section of the An example of the algorithm section of the page, the variable lambda (λ) is listed as limit on time iteration, but is not included anywhere else on this page. I'm guessing that its either the result of other info being edited out, or something that was copied in without careful review. —The preceding unsigned comment was added by Special:Contributions/ (talk)

 * I fixed this by adding a reference to lambda in the text. However, there is still an inconsistency -- the text mentions Θ(v,t), which I think is the neighbourhood function at time t and vector position v with relation to the current BMU.  But the variables section doesn't mention any reliance on v (it has Θ(t)). —The preceding unsigned comment was added by Special:Contributions/ (talk)

Examples
I removed "gnod, a Kohonen network application." because I don't see any evidence saying that it is and on the gnod page, there are references to sites that say it's not. I added WEBSOM, because it is. --JamesBrownJr 22:47, 2 March 2007 (UTC)

Mapping higher dimensional spaces into lower ones
Added: ", as an artificial neural network," to paragraph two because Prof Kohonen, by no means, invented the idea of mapping higher dimensional spaces into lower ones, which is what the previous existing language of that paragraph implied....June 15, 2007 —The preceding unsigned comment was added by Special:Contributions/ (talk)

The network structure
IMHO, it's confusing that this section describes SOM as a feedforward network. In a typical feedforward network, there are multiple layers and weights affect the extent to which output values from neurons in one layer affect the inputs to neurons in the next layer. But if I understand SOM correctly (which may very well be the problem here), SOM has only one "layer" of neurons. Values are never "fed forward" (as there's no next layer to feed them to), and the "weights" in SOM have a completely different role than the weights in a typical feedforward network. I don't understand the statement "Each input is connected to all output neurons" because there is no input layer of neurons. Each vector (aka pattern) from the training dataset will affect the BMU and its neighbors, but this is not same as being "connected to all output neurons". (If my understanding is incorrect, please delete this comment.)

Contradiction with Generative Topological Map article
The following appears to contradict what is said in Generative Topographic Map about topology preservation."It is trained using unsupervised learning to produce low dimensional representation of the training samples while preserving the topological properties of the input space."

I would say that it cannot preserve the topological properties of the input space for all possible inputs. Perhaps you should change the sentence to: "It is trained using unsupervised learning to produce low dimensional representation of the training samples while trying to preserve the topological properties of the input space."

The opinion that this contradicts the GTM article is not accurate. Both algorithms can be expected to produce topological error; it is therefore a matter of degree. Typically one would run the SOM algorithm several times and measure the topological error. Depending on how important this issue is for the analyst, he or she would select the map with the lowest topological error. I am removing the contradiction warning but I will add more information on SOM vs GTM. —Preceding unsigned comment added by ElectricTypist (talk • contribs) 15:48, 21 November 2007 (UTC)

Awesome reference
I here by state this article as 'awesome', its a good reference for anyone who wants specific information reguarding the workings of this type of neural network, instead of a smear of general information and no useful engineering qualities at all. --Chase-san 11:28, 4 August 2007 (UTC)

 * It's a good article, certainly. I don't understand "toroidal grids", "U-matrices" or such but this vector stuff made me understand the general principles. I think I might be able program some kind of SOM based on the article. ... said: Rursus (bork²) 20:29, 2 May 2009 (UTC)

Picture
Without any kind of description and context, those pictures are completely meaningless. What do the colours mean? What is the form of training data? What are the inputs? How do you generate the image from the final sets of weight vectors? How do you interpret the pictures. Deeply non-awesome. -- GWO —Preceding unsigned comment added by Gareth Owen (talk • contribs) 12:44, 12 September 2007 (UTC)
 * True. I have added a description of what is in the picutre. There's not enough space to describe all that you ask for - a larger article section would be required for that. It is however a standard visualization style for SOMs. In the external links section there are a bunch of references that go deeper into SOM visualization. --Denoir 18:55, 20 September 2007 (UTC)
 * I would like to see some explanation of what you can learn from this visualiztion. Otherwise, it just looks like a pretty picture with a link to a product. --Skremer (talk) 11:55, 7 January 2008 (UTC)

Topography vs. Topology
ITEM 1.

The first paragraph of the article contains the statement that "The map seeks to preserve the topological properties of the input space." This is a reasonable aim, but one that is virtually impossible with the SOM on all but the most trivial of data. It also gives the impression that the SOM generates a topology preserving map.

To improve the article, the sentence "The map seeks to preserve the topological properties of the input space." should be replaced with "The SOM map aims to exploit the topographic relationships of the network nodes to provide more information about the underlying data space than is possible with the regular Vector Quantisation approach."

ITEM 2.

"Interpretation There are two ways to interpret a SOM. Because in the training phase weights of the whole neighborhood are moved in the same direction, similar items tend to excite adjacent neurons. Therefore, SOM forms a semantic map where similar samples are mapped close together and dissimilar apart."

This last sentence is misleading and wrong. This is only true if there is no violation in the topological mapping of the SOM map. Graph dimensionality, graph size and graph folding can cause violations in the SOM mapping.

Let me expand on this:

Neural maps aim to exploit the topographic relationships of the network nodes to provide more information about the underlying data space than is possible with the regular Vector Quantisation approach. The neural map aims to 1. link the relationships between input data with the relationships between the nodes of the graph, and 2. for the map to be truly useful, the relationships between nodes of the graph should be reflected in the relationships within the input data. This is very important, and is where the SOM approach simply fails on all but the the most trivial of data. In topology preserving mappings, neighbourhoods are preserved in the transformations from data to graph space and vice-versa.

I suggest anybody interested in why the SOM can not be considered a topological mapping reads [H. U. Bauer, M. Herrmann, and T. Villmann. Neural maps and topographic vector quantization. Neural Networks, 12:659-676, 1999]. The SOM (at best) is a topographic mapping - it is not a topological mapping. The Growing Neural Gas algorithm [B. Fritzke. A Growing Neural Gas Network Learns Topologies. In G. Tesauro, D.S. Touretzky, and T.K. Leen, editors, Advances in Neural Processing Systems 7 (NIPS'94), pages 625-632, Cambridge, 1995. MIT Press.] (tends to) generate a topology preserving mapping. This is a well known fact, and this article is misleading with its incorrect use of terminology.

To improve this article, "Therefore, SOM forms a semantic map where similar samples are mapped close together and dissimilar apart." needs much more work. This statement is only true if the map contains no topographic errors, which is difficult to achieve on all but the most trivial of data.

FORTRANslinger (talk) 20:05, 19 December 2007 (UTC)

History section
Can somebody explore on the history of the subject?

It must be at least, starting 1982. However, there must be a chronological list of related subjects developed before SOM. (k-means, hard c-means, Linde-Buzo-Gray algorithm and other clustering stuff?) —Preceding unsigned comment added by Arkadi kagan (talk • contribs) 21:33, 19 January 2010 (UTC)

Perhaps, some precise info signed by Teuvo Kohonen: The Self-Organizing Map algorithm was introduced in 1981. The earliest applications were mainly in engineering tasks. Later the algorithm has become progressively more accepted as a standard data analysis method in a wide variety of fields ...  Arkadi kagan (talk) 08:43, 20 January 2010 (UTC)

Improper Reference
One of the references is password-protected. This does not seem appropriate for WP: Rmkeller (talk) 06:17, 2 November 2010 (UTC)
 * 1) ^ Ultsch A (2003). U*-Matrix: a tool to visualize clusters in high dimentional data. University of Marburg, Department of Computer Science, Technical Report Nr. 36:1-12.

Another Improper Reference
I was interested in the reference supporting this sentence: "It has been shown that while self-organizing maps with a small number of nodes behave in a way that is similar to K-means, larger self-organizing maps rearrange data in a way that is fundamentally topological in character. [5]" However it points to the website http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Self-organizing_map.html, which is a mere copy of this wikipedia article.... how could that happen? — Preceding unsigned comment added by 141.14.31.91 (talk) 10:48, 28 January 2015 (UTC)

Neural network?
Why is the self-organizing map considered to be a type of artificial neural network? What is it that is "neural" about them? —Kri (talk) 12:55, 2 January 2017 (UTC)

time adaptive self-organizing map
The link for this just brings you back to the SOM page. Either the link should be removed or an article for TASOMs should be written (latter is ideal).

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Talk:Self-organizing map


text:
Talk:Steve Jackson Games

Untitled
Removed this contact info:
 * Their phone number is 512-447-7866. Their fax is 512-447-1144. Their general e-mail address is [mailto:sjgames@io.com sjgames@io.com]. Their mailing address is PO Box 18957, Austin TX 78760. Their shipping address is 2700-A Metcalfe, Austin, TX 78741-5630.

It is not encyclopedic (IMHO) and can be found on their web site. Their site is a better place for this kind of info since it may change. -Frecklefoot

So why DID the raid happen?
The article only mentions the -mistaken- reasons for the raid, and that everything about it being a part of Operation Sundevil was false, even if common perception by the public... ...so.... what WAS the real reason for the raid? You'd think, being an encyclopedia article, this would be mentioned... or does nobody know why they raided? --I am not good at running 01:38, 29 November 2005 (UTC)

The Steve Jackson Games website has their account of what happened at http://www.sjgames.com/SS/, and a retyped (not by them, apparently) copy of the secret service affidavit at http://www.sjgames.com/SS/affidavit.html. The reason (after a brief glance) appears to be that one of the writers of GURPS: Cyberpunk ran a BBS that the sercret service believed had illegally reposted/ distributed the Bell South E911 Practice text file which had been stolen and not legal to distribute. 66.93.216.231 19:14, 3 February 2006 (UTC)

 * Although the Bell South E911 practice text file was available from Bell South on request for $13.00 which came out in the trial. Originally Bell South pressured the Secret Service that the file was proprietary information, this was found later to be untrue. Timmccloud 22:09, 15 May 2007 (UTC)

Unencyclopedic list tag
What exactly is "unencyclopedic" about the list of games produced by this company? It seems highly relevant and is organized in a reasonable manner. I plan on removing the tag in one week unless someone can explain why it should stay. -Chunky Rice 20:37, 30 August 2007 (UTC)

Links for Dice games
User 75.167.196.110 has added three newish dice games to the article. (Thanks!) For easy of reference, here are the pages at SJG's website: Cthulhu Dice, Zombie Dice, Proteus. Cheers, CWC 09:50, 9 June 2010 (UTC)

title: Talk:Steve Jackson Games


text:
Secretary of State for Northern Ireland

The secretary of state for Northern Ireland (Rúnaí Stáit Thuaisceart Éireann; Secretar o State for Norlin Airlan), also referred to as the Northern Ireland secretary or SoSNI, is a secretary of state in the Government of the United Kingdom, with overall responsibility for the Northern Ireland Office. The officeholder is a member of the Cabinet of the United Kingdom. The incumbent secretary of state for Northern Ireland is Hilary Benn.

The office holder works alongside the other Northern Ireland Office ministers. The corresponding shadow minister is the shadow secretary of state for Northern Ireland.

History
Historically, the principal ministers for Irish (and subsequently Northern Ireland) affairs in the UK Government and its predecessors were:
 * the Lord Lieutenant of Ireland (c. 1171–1922);
 * the Chief Secretary for Ireland (1560–1922); and
 * the Home Secretary (1922–1972).

In August 1969, for example, Home Secretary James Callaghan approved the sending of British Army soldiers to Northern Ireland. Scotland and Wales were represented by the secretary of state for Scotland and secretary of state for Wales from 1885 and 1964 respectively, but Northern Ireland remained separate, owing to the devolved Government of Northern Ireland and Parliament of Northern Ireland.

The office of secretary of state for Northern Ireland was created after the Northern Ireland government (at Stormont) was first suspended and then abolished following widespread civil strife. The British government was increasingly concerned that Stormont was losing control of the situation. On 30 March 1972, direct rule from Westminster was introduced. The secretary of state filled three roles which existed under the previous Stormont regime:
 * the governor of Northern Ireland (the nominal head of the executive and representative of the British monarch)
 * the prime minister of Northern Ireland (in the present day, a role filled by the first minister of Northern Ireland and deputy first minister of Northern Ireland acting jointly)
 * the minister of home affairs (in the present day, a role filled by the minister of justice).

Direct rule was seen as a temporary measure, with a power-sharing devolution preferred as the solution, and was annually renewed by a vote in Parliament.

The Sunningdale Agreement in 1973 resulted in the brief existence of a power-sharing Northern Ireland Executive from 1 January 1974, which was ended by the loyalist Ulster Workers' Council strike on 28 May 1974. The strikers opposed the power-sharing and all-Ireland aspects of the new administration.

The Northern Ireland Constitutional Convention (1975–1976) and Northern Ireland Assembly (1982–1986) were unsuccessful in restoring devolved government. After the Anglo-Irish Agreement on 15 November 1985, the UK Government and Irish Government co-operated more closely on security and political matters.

Following the Belfast Agreement (also known as the Good Friday Agreement) on 10 April 1998, devolution returned to Northern Ireland on 2 December 1999. This removed many of the duties of the Secretary of State and his Northern Ireland Office colleagues and devolved them to those locally elected politicians who constitute the Northern Ireland Executive.

Formerly holding a large portfolio over home affairs in Northern Ireland, the current devolution settlement has lessened the secretary of state's role, granting many of the former powers to the Northern Ireland Assembly and Northern Ireland Executive. The secretary of state is now generally limited to representing Northern Ireland in the UK cabinet, overseeing the operation of the devolved administration and a number of reserved and excepted matters which remain the sole competence of the UK Government e.g. security, human rights, certain public inquiries and the administration of elections.

Created in 1972, the position has switched between members of Parliament from the Conservative Party and Labour Party. As Labour has not fielded candidates in Northern Ireland, and the Conservatives have not had candidates elected to the Northern Ireland Assembly or for House of Commons seats in the region, those appointed as secretary of state for Northern Ireland have not represented a constituency in Northern Ireland. This contrasts with the secretary of state for Scotland and the secretary of state for Wales.

The secretary of state officially resides in Hillsborough Castle, which was previously the official residence of the governor of Northern Ireland, and remains the royal residence of the monarch in Northern Ireland. The secretary of state exercises their duties through, and is administratively supported by, the Northern Ireland Office (NIO).

The devolved administration was suspended several times (especially between 15 October 2002 and 8 May 2007) because the Ulster Unionist Party and Democratic Unionist Party were uncomfortable being in government with Sinn Féin when the Provisional Irish Republican Army had failed to decommission its arms fully and continued its criminal activities. On each of these occasions, the responsibilities of the ministers in the Executive then returned to the Secretary of State and his ministers. During these periods, in addition to administration of the region, the Secretary of State was also heavily involved in the negotiations with all parties to restore devolved government.

Power was again devolved to the Northern Ireland Assembly on 8 May 2007. The secretary of state retained responsibility for policing and justice until most of those powers were devolved on 12 April 2010. Robert Hazell has suggested merging the offices of secretary of state for Northern Ireland, for Scotland and for Wales into one secretary of state for the Union, in a department into which Rodney Brazier has suggested adding a minister of state for England with responsibility for English local government.

List of secretaries of state for Northern Ireland
Colour key

title: Secretary of State for Northern Ireland


text:
Per Albin Hansson

Per Albin Hansson (28 October 1885 – 6 October 1946) was a Swedish politician, chairman of the Social Democrats from 1925 and two-time Prime Minister in four governments between 1932 and 1946, governing all that period save for a short-lived crisis in the summer of 1936, which he ended by forming a coalition government with his main adversary, Axel Pehrsson-Bramstorp.

Political activity
During World War II, in which Sweden maintained a policy of neutrality, he presided over a government of national unity that included all major parties in the Riksdag with the exception of the Communist Party. Forging the Social Democratic grip on Swedish politics that would last throughout the century, Hansson left an astounding legacy on his party as well as creating the idea of Sweden to become "Folkhemmet", "The People's Home". This remained intact until the early 1990s, including a strict policy of neutrality, a wide-stretching welfare state through parliamentary legislation, and reformist social corporatism rather than Marxist socialization of the means of production. Following the war, Hansson formed a Social Democratic cabinet enjoying absolute majority in the Riksdag before succumbing to a heart attack on his way home from work late at night on 6 October 1946.

During Hansson's fourteen years as Prime Minister of Sweden, a wide range of reforms were realised, such as subsidised dental care, income-tested child allowances for invalidity pensioners and widows, maternity allowances through voluntary sickness insurance, and a 1935 law that introduced state subsidies for the construction of apartment houses for families with three or more children, combined with housing allowances for families with more than two children living in these houses.

A bill that provided for "the establishment of a voluntary unemployment insurance scheme was passed into law and came into force on 1 January 1935." The Government also allocated funds for the improvement of rural housing. An act of 26 June 1936 amended that of 1929 "so as to include all the diseases contained in the revised Convention, as well as those due to carbon monoxide, cyanogen and its compounds, chlorine, nitrous fumes, chromic acid and its compounds, and certain infectious diseases (hospital staffs, etc.)." A People's Travel Association was founded for workers and their families in March 1937. An act of 11 September 1936 "contains a new regulation of the right of association and collective bargaining. The act applies not only to workers in private undertakings but also to employees in the service of the State or the communes who have not the status of officials." On 1 November 1936 an act came into force "regulating hours of work on farms employing more than four workers, exclusive of cattle tenders. The maximum working day is 10 hours, and the net working week may vary from 46 to 56 hours in the course of the year." According to one study, the years 1937 to 1939 became "a harvest season for a series of social reforms that previously for the most part were dreams for the future."

Writing on these years, Hansson stated that "1937 loosened things up. That is when a pension amendment indexed to the cost of living was enacted, child support, mothers’ assistance, maternity assistance, far-reaching improvements in preventative mother and child care, the housing loan fund. The regulation of farm labor was approved. 1938 gave us compulsory holidays, the national dental plan, and the Institute for Health Insurance. 1939 saw the regulation of working hours … [and] housing for pensioners was created for the aged."

An act to provide for 12 days of annual holiday with pay for workers passed the Riksdag on 2 June 1938, while a Royal Notification of 2 December 1938 "deals with medical inspection of workers exposed to silicosis, referring to: examination on engagement and annually thereafter; practical methods to be followed; medical authorities entrusted with examination; recording of results on the health register, etc."

The Workers' Protection Act of 1912 was "amended and extended to cover certain aspects of hygiene and protection for young persons even in the smaller undertakings, as well as medical examination for adults on engagement and periodically thereafter in the case of particularly unhealthy trades, notably those involving exposure to lead poisoning and to silicosis." Also, under legislation of ("act of 3 June 1938, notification of 17 June 1938") "compensation has been extended to cover forms of dermatitis due to the use of chlorinated derivatives of phenol for impregnating wood."

A 1938 act amended the Workers' Protection Act, with an Institute of Social Hygiene set up; one of its duties being the study of maternity protection. An act of 1938 authorised "loans and grants for the erection of roomy accommodation for large families living in overcrowded buildings in rural districts." The 48-hour week "has been extended to cover the staff in lunatic asylums and the Government has fixed the increases in staff which this reform involves." The Holidays with Pay act, which was promulgated on 17 June 1938, "contains special provisions for home workers." This act "introduced a legal system of annual holidays with pay in the country. The act, which is of general application, grants one working day's holiday for every month of service after one year, provided that at least 180 days have been worked in the same undertaking and at least 16 days per month; the act may not be used to invalidate any more favourable conditions contained in collective agreements. For seamen in particular the payment during the holiday includes wages and an allowance for food. Changes in the ownership of the vessel and interruptions of service for which the seaman is not responsible do not affect the right to the holiday."

A new act fixed hours of work for employees in commerce. From 1 January 1939 the working hours for nursing and domestic staff were 48 in the week, and on 10 March 1939 "the Government presented a Bill to amend the act of 16 May 1930 on hours of work in bakeries. The proposed amendments would enable Sweden to ratify the international Convention on the subject. They suppressed the exemption of family undertakings from the scope of the act and the provisions under which the act applied only to the production of bread and pastry for sale. The Bill was passed by Parliament on 11 May 1939." Instructions concerning the inspectorates for electrical installations, explosives and ships were published on 30 June 1939 and other instructions on the inspection of lifts on 13 December 1939. Three Royal Notifications of 26 January 1940 "amended the existing regulations on the special inspection of the State railways, private railways and explosive substances." The war risks of seamen in the event of accidents were dealt with in an act of 11 June 1937, which provided "for a very considerable increase in the accident benefits normally due to seamen if the injury or death results from an act of war. In the event of total incapacity or death the individual is entitled to a lump sum which, in the case of officers, is generally equal to twelve months' salary, and in the case of all other ratings, 4,800 kr. For partial incapacity the sum is proportionately reduced." An act of 14 October 1939 provided that "no person may be discharged from employment on account of military or other service which he is required by law to perform. The parties may however agree to override this rule if the military service is to last more than three months." An act of 19 May 1939 prohibited employers "from discharging, owing to engagement or marriage, any wage earner with at least two years' continuous service in the undertaking. Any agreement to the contrary is null and void and an employer who contravenes this rule must pay damages. The act applies to undertakings employing at least three persons."

Early life and career
Per Albin Hansson was born in Kulladal, a neighborhood in Malmö, Sweden, on 28 October 1885.

One of the first professional politicians of Sweden, Hansson participated in the creation of the Swedish Social Democratic Youth in 1903 and presided over it as its chairman in 1908–09, a period in which universal suffrage and proportional representation was to be gradually enacted for all Swedish males by Conservative Prime Minister Arvid Lindman, later a rival of Hansson. Influenced generally by Karl Kautsky's views on socialism, Hansson succeeded Hjalmar Branting as editor of Social-Demokraten in 1917 and was appointed his Minister of Defence in Sweden's first Social Democratic cabinet in 1920, following a Liberal-Social Democratic coalition enacting equal suffrage for men and women (in effect as of the 1921 election). Per Albin Hansson held this office in all of Branting's three cabinets between 1920 and 1925 (years which saw eight governments), performing numerous cut-backs on the military budget. Upon Branting's death in 1925, Hansson rose to be embraced as chairman of the party. His legitimacy remained under dispute, however, and only in 1927 did he become the head of the Riksdag faction, before having been confirmed undisputedly as Branting's successor in a 1928 congress.

Upon losing power to Carl Gustaf Ekman's pro-prohibition Liberals in 1926, Hansson worked from the opposition bench and, although heading what was to remain the largest party of the Riksdag to date, faced a major setback upon cooperating with the Communists in the infamous election of 1928. Hansson's party did poorly as a result, and not until the 2010 election would the Social Democrats and the Communists (the latter changed its name, in 1995, to the Left Party) would the two parties run in tandem again.

In opposition to the Conservative – though equally pragmatic and staunchly anti-fascist – Lindman cabinet, Hansson pressed for the introduction of a welfare state rather than wide-scale nationalizations. He called his vision Folkhemmet ("the People's Home") in a Riksdag debate in 1928.

Following the fall of Ekman in 1932 due to a corruption scandal involving the recently deceased industrialist Ivar Kreuger, the Social Democrats made gains, which altogether gave them 104 Riksdag seats and 41.7% of the popular vote. Though this left them short of a majority, they benefited from the inability of the Liberal parties (themselves unable to form a single faction until 1934), the Conservatives and the Agrarians to form a stable administration of their own. This inability gave Hansson his chance. He courted and eventually obtained support from the Farmers' League, through promising an agriculture policy favoring the interests of the League (kohandeln), although he stopped short of giving League parliamentarians any cabinet posts.

In June 1936, the combined efforts of the Liberals, the Conservatives and the Agrarians brought the Hansson-led government to an end and ensured Hansson's own resignation as prime minister. Following Hansson's departure, League chairman Axel Pehrsson-Bramstorp was able to form a three-month "Vacation Cabinet". That lasted until the elections in September, which saw a rise in support of the Social Democrats. This time Hansson invited certain League members into the cabinet, and Pehrsson-Brahmstorp therefore became Minister of Agriculture. The administration enjoyed a substantial parliamentary majority that lasted until 1939.

World War II
Following the German-Soviet invasion of Poland in 1939, Hansson declared strict neutrality and called for the formation of a broad coalition government involving all major parties under his leadership, which was realized in December except only the pro-Stalinist Communist Party and its short-lived pro-German splinter faction, the Socialist Party. Alone in Europe save for Spain, Portugal, Switzerland, Ireland and the Vatican, Sweden maintained neutrality throughout all World War II, but like the mentioned countries, cooperated and traded with both sides. Winston Churchill claimed that Sweden during World War II ignored the greater moral issues and played both sides for profit, a criticism mimicked in criticism towards Sweden's policy towards the German occupation of Denmark and Norway upheld partly by transportation reinforcement through Swedish territory, sanctioned by Hansson's cabinet.

The German invasion of the Soviet Union on 22 June 1941, Operation Barbarossa sparked an ultimatum known as the Midsommarkrisen by the government of Nazi Germany to Hansson's cabinet, demanding some military concessions, including German troop transports on Swedish railways in order to support Germany's ally Finland. Political deliberations surrounding this ultimatum have been dubbed the "midsummer crisis", which ultimately, allegedly following King Gustav V's decision to resign should the concessions not be made, fell out in favor of the Axis. The 83-year-old king formally (although having not directly intervened in the government's policies since 1914) had the powers to appoint his own cabinet, and his open intervention in the issue was seen as a threat to the stability of the government and, given the ongoing war, to the sovereignty of the nation.

Recent research by Carl-Gustaf Scott argues however that there never was a "crisis" and that "the crisis was created in historical hindsight in order to protect the political legacy of the Social Democratic Party and its leader Per Albin Hansson."

To get the steel required by the German Ruhr and Upper Silesia industry, Germany was, in 1939–1940, dependent on shipments of Swedish iron ore, since access to the supplies from the mines in France, the traditional supplier, were cut off until the invasion of France. In 1939–1940 the Allies tried various ways to stop the shipments of Swedish ore, for example by mining Norwegian territorial waters.

In effect, the main political priority was to avoid direct war engagement of Sweden during World War II. Following Germany's setbacks around 1942–43, Sweden was no longer seriously threatened by an invasion from Nazi Germany and subsequently rolled back most of its concessions.

Death and political legacy
Following the surrender of Germany, Hansson wanted to maintain a Social Democratic-led coalition government of all non-Communist parties. However, he failed to achieve this as a result of strong opposition within his own party which favoured a radical reformist agenda following the war. Hansson reluctantly agreed to a single-party government. He had abandoned his early revolutionary and strictly anti-militarist views in favor of social corporatism, class collaboration and a reformist agenda involving few nationalizations but stable armed forces in order to secure neutrality. He died from a heart attack in Stockholm on 6 October 1946 while stepping off a tram at the Ålstens Gård station. He was succeeded as party chairman and prime minister by Minister of Education Tage Erlander, who held both offices concurrently until 1969, completing most of Hansson's legacy. Per Albin Hansson, seen often as the most successful prime minister in Swedish history. He is interred in Norra Begravningsplatsen in Stockholm.

Private life
Per Albin Hansson was married to Elisabeth Fryckberg between 1918–1926. Before marrying her, he lived with Sigrid Vestdahl and fathered one child by her in 1908. He continued his relationship with Vestdahl after his marriage to Fryckberg. He lived with and supported both families financially. This was most likely known to the press, but little was written about it. It appears both women were aware of the situation.

In popular culture
In the Swedish television movie Four Days that shook Sweden – The Midsummer Crisis 1941 from 1988, he is played by Swedish character actor Ernst-Hugo Järegård.

title: Per Albin Hansson


text: Talk:Connection/OldHistory

title: Talk:Connection/OldHistory


text:
Carmen Amaya

Carmen Amaya (2 November 1918 – 19 November 1963) was a Spanish Romani flamenco dancer and singer, born in the Somorrostro district of Barcelona, Catalonia, Spain.

She is often hailed as "the greatest Flamenco dancer ever" and "the most extraordinary personality of all time in flamenco dance." She was the first female flamenco dancer to master footwork previously reserved for the best male dancers, due to its speed and intensity. She sometimes danced in high-waisted trousers as a symbol of her strong character.

Biography
Carmen Amaya Amaya was born in Somorrostro, Spain, to a Romani family, her father José Amaya Amaya (aka. "El Chino", "The Chinaman"), a guitar player, and Micaela Amaya Moreno, her mother. Carmen was the second of eleven children, although only six (three sisters and two brothers) survived to adulthood. She is also the cousin of famed flamenco dancer La Chunga.

Her date of birth is disputed. Montse Madridejos and David Pérez Merinero name 1918 as her year of birth. They cite Barcelona's inhabitants list of 1930, in which a family Amalla with a 12-year-old daughter Carmen is mentioned. They claim that no birth document is available and the document of baptism was lost due to a church fire. Furthermore, a 1920 oil painting by Julio Moisés named Maternidad shows a mother with a 2-3 year old girl, supposed to be Carmen with her mother Micaela. According to them, photographs showing Carmen Amaya as a teenager also support 1918 as the year of birth. According to Montse Madridejos, professor of Music History at the University of Barcelona and a flamenco history researcher, who specializes in Carmen Amaya, her ethnicity could have also been a factor in the birth date ambiguity: "At that time, a gypsy was neither baptized, nor registered".

In 2023, the researcher Montse Madridejos published an academic article in the journal Sinfonía Virtual in which she underscores and gives more weight to 1918 as the possible year of birth of Carmen Amaya. Amaya entered the flamenco world accompanied by her father, an impoverished Calé Romani guitarist who made a living by playing in pubs day and night. When Carmen was a child, she started going out with her father at night. He accompanied her on the guitar while she performed. Afterwards, they begged and picked the small change that the public threw on the floor. Soon earned her first nickname, "La Capitana".

At the same time, she started to appear in some lesser known theaters. It was only after Josep Santpere, a bright variety show businessman, showed for the first time his interest in Carmen and introduced her to more prestigious venues, that she made her debut at the Spanish Theatre in Barcelona. Soon after, she was performing at the Palace Theatre in Paris.

The first time she appeared in print was in 1931 thanks to Sebastià Gasch, an art critic who saw her and wrote an article in the weekly newspaper Mirador (magazine). Sebastian Gash wrote:"'Suddenly a jump! And the gypsy girl danced. Indescribable. Soul. Pure Soul. Feeling made flesh. The floorboards vibrated with unprecedented brutality and incredible precision. La Capitana was a gross product of Nature. Like all gypsies, She must have been born dancing. It was before school, before the academy. All that she knows, She must have known from birth. Promptly, the viewer feels subjugated, upset, dominated by the face of La Capitana, by her fierce hip movements, by the bravery of her pirouettes and the force of her broken turns, whose animal ardor ran parallel with the astonishing accuracy with which she executed them. The raging battery of her heels and the unsteady play of her arms now aroused, excited, then collapsing, surrendered, abandoned, dead, gently moved by the shoulders, are still recorded in our memories like indelible plaques. what caused us to look at her dance was her nerve, which twisted her in dramatic contortions, her blood, her violence, her wild impetuosity as a caste dancer.'"

At this point Vicente Escudero, a respected businessman, saw her dancing and concluded that Carmen would bring about a flamenco revolution thanks to her perfect synthesis of two important styles: that of the traditional dancers, and the looming style of dancers in the varieties.

In 1930, she was part of the Manuel Vallejo company, performing all over Spain. On her return to Barcelona she danced at the Teatro Español, recommended by José Cepero.

That year she worked in the Zarzuela Theatre, also known as the Coliseum, in Madrid with Conchita Piquer, Miguel de Molina, and other famous artists, and at the Fontalba Theatre. That was the authentic success of Carmen nationwide. She played a small role in La hija de Juan Simón and Maria de la O, and worked for a musical magazine in Barcelona. From her first performance" in 1935 to her last one in "Los Tarantos", her dancing showcases the purest form of flamenco. The films she starred in are remarkable in that very few films have been created around one figure. They are also a model for all dancers who define their dance as being "of temperament". Very seldom in the history of New York have dance and flamenco been as successful as Carmen Amaya's performances.

Juan Carceller hired her for a tour. She travelled to several big cities, including San Sebastián. In 1935, Luisita Esteo presented her in Madrid, in a show at the Coliseum. On 18 July 1936, when the coup in Spain took place, Carmen and her team were in the Zorrilla Theatre in Valladolid, working for Carcellé's company. At that time, they were financially secure and she had bought her first car. They were due to go to Lisbon to sign the lease, but the car was requisitioned and they could not travel to Portugal until November.

Beginning of international success: Latin America (1936–1940)
In 1936, when the Spanish Civil War had just begun, Carmen Amaya and her troupe were on tour in Valladolid with Luisita Esteso's show. They crossed the border from Spain to Portugal and, after a short time arrived in Lisbon. From there they sailed for Buenos Aires on the ship Monte Pascoal, which took fifteen days to cross the Atlantic and arrive at Brazil and Uruguay. She debuted in Buenos Aires, accompanied by Ramón Montoya and Sabicas at the Maravillas Theatre.

During this stage of her life, she added to her artistic group several members of her family. She made films in Buenos Aires with Miguel de Molina and won the admiration of musicians Arturo Toscanini and Leopold Stokowski, who publicly praised her.

The success of Carmen Amaya and her family exceeded all expectations. They planned to stay for only four weeks but ended up staying there for nine months, since every time Carmen performed, the theater was filled and tickets were sold out two months in advance. A good example of the enormous popularity that the artist achieved in this South American country is the construction of a theater that bears her name: el Teatro Amaya.

In addition, it seems that during most of those years in America the bailaora maintained a personal relationship with Sabicas, who declared shortly before his death that he and Carmen had been dating for nine years, and that they had split in Mexico.

Consolidation in the United States (1941–1947)
In the US, Carmen Amaya met many of the most influential people of her time. She went several times to Hollywood to film some movies and the most important personalities of cinema, music or culture wanted to see her dance. The musician Toscanini saw one of her performances once and declared that he had never seen an artist with more rhythm and more fire. She improvised continuously, as quickly as perfectly.

She traveled to New York in 1941 and performed at Carnegie Hall with Sabicas and Antonio de Triana. Whilst in the United States, she also met Franklin Roosevelt, President of the United States. It was reported that after seeing her, Roosevelt gave her a bowling jacket with brilliants and invited her to dance at the White House. She returned to Europe where she performed at the Théâtre des Champs-Élysées in Paris and later in London, where she got to meet the Queen of the United Kingdom.

Return to Spain
When Carmen Amaya returned to Spain in 1947, she was already a world-famous figure. In the years spent in America she not only professionally established herself as an artist, but also became, inevitably, a legend. By then, her dance was the most daring flamenco ever performed in a theater. However, she did not stand out only for her art but also for her fascinating personality, which won over everyone she knew, both because of her dancing and her unpredictable behaviour. She also was extraordinarily generous.

She was a great success at the London Princess Theatre in 1948, and also on her next American tour. She toured Argentina again in 1950.

She returned to dance in Spain the following year, performing at the Tivoli theatro in Barcelona after several performances in Rome. She continued her work in Madrid, Paris, London, and different cities in Germany, Italy, and the rest of Europe. The Queen of England congratulated her when she performed there; Carmen Amaya and Elizabeth II appeared together in a newspaper photograph entitled: "Two queens face to face."

In 1951, she married guitarist Juan Antonio Agüero, a member of her troupe, coming from a distinguished family from Santander, who was not a gypsy. They lived an authentic love story and celebrated an intimate wedding. In 1959, Carmen experienced one of the most exciting moments of her life, when the inauguration ceremony of a fountain bearing her name was held. The fountain was placed on the Paseo Marítimo de Barcelona, which crosses the neighbourhood of Somorrostro, the same places where she had walked by many years before as a child, barefoot and dragging her misery.

In subsequent years she continued her work in northern Europe, France, Spain, the United States, Mexico and South America. She triumphed at the Westminster Theatre in London and at La Zarzuela theatre in Madrid in 1959. At that time, Barcelona paid tribute to Carmen Amaya by building the Carmen Fountain in the artist's old home district, Somorrostro, to popular acclaim.

She recorded her last film, Los Tarantos, by Rovira-Beleta in 1963, and afterwards continued working. At the end her illness, a kind of renal impairment that impeded her properly eliminating the toxins that her body accumulated, prevented her from continuing in Gandía.

Her illness was exacerbated by the filming of her latest film, Los Tarantos, directed by Rovira-Beleta (1963). Carmen overcame her health issues and at the end of filming started a summer tour. The last time she performed in Madrid, she was already terminally ill. Finally, her illness stopped her from performing. The doctors could not find a suitable treatment. She danced for the last time in Malaga. On 8 August 1963, whilst she was working in Gandía, Carmen interrupted her performance. She was dancing when suddenly she said to Batista: "Andrés, we finished."

Death
Carmen Amaya died of kidney disease in Begur, Girona, Catalonia, northeast Spain, in 1963 and is buried at the Cemetery of Ciriego in Santander. She was awarded the Medal of Merit of Tourism in Barcelona, the Lasso of the Lady of the Order of Isabel la Católica award, and given the title of Adoptive Daughter of Begur.

Three years after her death (1966) she was honored by a monument placed in the Amusement Park of Montjuic. Buenos Aires has a street named after her. In Madrid in the "Tablao" Los Califas, she was honored by a tribute performance in which many artists participated, including Lucero Tena, Mariquilla, and Felix de Utrera.

In 1988, as an homage to Carmen Amaya, the Tablao de Carmen was founded in the Poble Espanyol, the very place where she danced for the King of Spain Alfonso XIII during the inauguration of the 1929 Barcelona International Exposition. Tablao de Carmen displays some of the photographic legacy of Carmen Amaya. The guitar of her husband Juan Antonio Agüero (by Santos Hernández 1930) is a part of the patrimony of the founder family of Tablao de Carmen and it is played in the Tablao on special occasions.

Medals and recognition awards
Her death was a great loss for the entire Flamenco world. She was awarded with the Medalla del Mérito Turístico de Barcelona, Lazo de Isabel la Católica and the title of Hija Adoptiva de Bagur. Her funeral summoned a large number of Roma People from different parts of Spain and even France.

Amaya died in Bagur, where she spent her last days, her remains rest in the crypt of her husband's family, in Santander. Three years after her death in 1966, the statues of her were erected in the Parque de Montjuic in Barcelona, and in Buenos Aires, while in Madrid, in Tablao Los Califas, a tribute, led by Lucero Tena, among other artists, took place. She was also honored in Llafranch (Girona) in 1970.

The personality of Carmen Amaya has been celebrated by critics, flamencologists and writers, as well as by poets, including Fernando Quiñones, author of the poem Soneto y letras en vivo para Car men Amaya. A selected transcription of these comments by Vicente Marrero, reads: ''Carmen Amaya can see the amazing conviction that sometimes tends to dance. "Gitanilla" ungainly, skinny, petite, almost disembodied. Brunette, with a tragic and remote idol face, Asian cheekbones, with long eyes full of omens, twisted arms. With her "repajolera" gypsy [Romani] grace, she is not just another millionaire in North America, but one of our great dancers, who has succeeded, with the secret of dance and her dance she was born to dance, and she danced  phenomenally. Carmen Amaya, is her name, is not a different woman in each of her dances, as so often happens with other great dance figures.''

''"Carmen Amaya can see the amazing conviction that sometimes tends to dance. "Gitanilla" ungainly, skinny, petite, almost disembodied. Brunette, with a tragic and remote idol face, Asian cheekbones, with long eyes full of omens, twisted arms. With her "repajolera" gypsy [Romani] grace, she is not just another millionaire in North America, but one of our great dancers, who has succeeded, with the secret of dance and her dance she was born to dance, and she danced  phenomenally. Carmen Amaya, is her name, is not a different woman in each of her dances, as so often happens with other great dance figures." ''

Carmen's flamenco legacy is still valid to this day as an example of dancing with force, meter, intensity and power and a way of expression which brought an end to the sweetness of flamenco which had endured until that point. The famous producer Sol Hurok described Carmen as "The Human Vesuvius." Carmen Amaya has been the incarnation of the flamenco dance par excellence. She has danced in numerous films.

On 2 November 2023, Google celebrated her 110th birthday with a Google Doodle.

Selected filmography

 * 1929 - La bodega (Wine Cellars)
 * 1934 - 2 mujeres y 1 Don Juan
 * 1935 - La hija de Juan Simón
 * 1935 - Don Viudo de Rodríguez
 * 1936 - María de la O
 * 1939 - Embrujo del Fandango (Cuba)
 * 1941 - Original Gypsy dances
 * 1942 - Aires de Andalucía
 * 1942 - Panama Hattie
 * 1944 - Knickerbocker Holiday (Pierna de Plata)
 * 1944 - Follow the Boys (Sueños de Gloria)
 * 1945 - Los amores de un torero (México)
 * 1945 - See My Lawyer (Entiéndase con mi abogado)
 * 1953 - When Do You Commit Suicide? (1953 film)
 * 1954 - Dringue, Castrito y la lámpara de Aladino
 * 1955 - Música en la Noche
 * 1963 - Los Tarantos

title: Carmen Amaya


text:
Talk:Design by contract

Opening heading
Ada needs to be added to the list of langs. Im suprised it is not there in a dbc article!

The two versions of this article need merging.

The executability of contracts is more a feature of "Programming By Contract". DBC is about software design, and so the executability of the contracts is not really relevant, and it's certainly not the primary way in which DBC is novel. Also, the difference between contracts and assertions is not merely a matter of "depth". The big deal with DBC is that the whole design of the system is based on the contracts, whereas C assertions are just sprinkled around in a rather ad-hoc manner and don't necessarily affect the system's design. Doradus — Preceding undated comment added 07:00, 25 July 2003 (UTC)

DBC failure causing hard failures.
Its not a DBC issue that is the concern.

If any program has an error and fails it is a problem.

However, if a program has an error and continues on blindly, that is some circumstances even worse.

The assumption of those anti-dbc is that if our program accepts faults blindly, and carries on, then less harm will happen compared to the program failing. This assumption is false because it implies some analysis of the problem, which clearly hasn't happened because of the exception.

eg. A square root function is called with a negative number. The system fails. The called function cannot determine what to do, since it doesn't know its context. The only way to make a decision as to what to do is more analysis.

If you are careful, you can put in place a top level error handler that does something sensible. This is for DBC or non DBC.

The non DBC solution would be return something, anything, and hope everthing works.

 * There is a middle ground. If there's some way to tell what objects have probably been corrupted, then that subsystem could be shut down somewhat cleanly, and perhaps even re-initialized.  For instance, if you're talking about a database interface, then each transaction could be wrapped with an exception handler that rolls back the transaction, cleans up some data structures, and reports an error in the appropriate manner.  The functionality that led to the exception could be disabled until an admin re-enables it.  And so on.  --Doradus 20:24, 31 January 2005 (UTC)

Assertions not strong enough
Let's stick to the Sqrt(-1) idea. Suppose we have a Math class that has a Sqrt function, defined in pre/post conditions:

pre: x >= 0 post: Sqr(result) == x

This looks like a good contract. Now a smart person inherits the Math class, and derives a ComplexMath class, which can handle complex numbers in addition to real numbers. The Sqrt function would look like:

pre: post: Sqr(result) == x

So now we have a weaker precondition and a stronger postcondition. Nothing surprising, but suppose we have some code that says:

Math math = new ComplexMath; i = math.Sqrt(-1);

Now what should this do - should it compile, run, crash or what? Any implementation using assertions would simply call ComplexMath.Sqrt and return a complex number. But that is not the contract the client intended to use. This code should should not be allowed to pass any Q.A. test, because the programmer expected Math behaviour and not ComplexMath. There's no telling what will happen if the next part of the program gets the complex result.

So because the client uses the Math contract (interface) here by declaring math as Math, the preconditions and postconditions of Math should apply too.

 * That is a good observation. Clearly, I agree with you.  There's an extensive Usenet thread on the topic.  (Look especially at article 74 which, I think, sums up the concensus that we all reached in that thread.) (Links removed because they triggered Wikipedia's stupid spam filter; see old version.)

 * I'm not sure how (or even if) it should be incorporated into the article though. --Doradus 16:46, 2 September 2004 (UTC)

Static Typing
In my book (figure of speech), static typing is a way of enforcing preconditions for a function at compile time, because it enforces the need that (for instance) the parameter x is always an integer. Do other agree with this view?

 * I agree, for whatever that's worth. That's exactly why covariant parameter redefinition is controversial: it's equivalent to strengthening a precondition.  --Doradus 20:16, Jan 31, 2005 (UTC)

 * Shure it is. And static typing can be used for invariants as well - for example with ranges. So I wonder if languages like with powerfull static typing (i.E. Ada) should be considered DOC as well. -- Krischik 07:02, 1 February 2005 (UTC)

title: Talk:Design by contract