Dr Pierre-Antoine Arrighi

Prof Pascal Le Masson
email: pascal.le_masson@mines-paristech.fr

Prof Benoit Weil

Dr Akin Kazakçi

TOOLS FOR INDUSTRIAL DESIGN WITH DESIGN THEORY -STYLE MODELS FOR MASS SINGULARITY."

Keywords: computer-aided design (CAD), industrial designers, engineers, 3D artists, conceptual models

According to some casual observers,computer-aided design (CAD) tools are very similar. These tools are used to design new artifacts in a digital environment;hence, they share typical software components, such as a computing engine and human-machine interface. However, CAD software is dedicated to specific professionals-such asengineers, three-dimensional (3D) artists, and industrial designers(IDs)-who claim that, despite their apparent similarities, CAD tools are so different that they are not substitutable. Moreover, CAD tools do not fully meet the needs of IDs. This paper aims at better characterizing CAD tools by taking into account their underlying design logic, which involves relying on recent advances in design theory. We show that engineering CAD tools are actually modeling tools that design a generic variety of products; 3D artist CAD tools not only design but immediately produce single digital artefacts; and IDCAD tools are neither a mix nor an hybridization of engineeringCAD and 3Dartist CAD tools but have their own logic, namely to create new conceptual models for a large variety of products,that is, the creation of a unique original style that leads to a generic singularity. Such tools are useful for many creative designers beyond IDs.

Introduction

This paper is based on a dual motivation. First, there is an industrial motivation.It is now wellknown that design processes should integrate different design professionals, such as industrial designers, engineers, and graphic designers. It is also wellknown that this integration must be supported by contemporary computer-aided design (CAD) tools that are currently at the basis of almost every design process. However, at the present time, every profession has, to some extent, its own CAD tools, with only limited compatibility. The question is whether it is possible tointegrate these tools.Initially, all these professional CAD tools appear very similar;in the literature on CAD, the focus is mostly oriented toward the technologies and algorithms for generating the artifact [START_REF] Stergiopoulos | Design of a 2-finger hand exoskeleton for VR grasping simulation[END_REF][START_REF] Dyn | Four-point curve subdivision based on iterated chordal and centripetal parameterizations[END_REF][START_REF] Mandil | Geometrical tools for the description and control of functional specifications at the conceptual design phase[END_REF][START_REF] Bodein | Decisional model for KBE implementation in a commercial CAD software[END_REF].Despite these apparent similarities, there are great discrepancies in professional CAD development. Engineering CAD and three-dimensional (3D)artist CAD are wellestablished and improve continuously whereas, in a type of blurred middle ground, industrial designers (IDs) are at the center of a great number of proposals and innovative tools (e.g., Rhino3D and Alias), but there are still debates about the inadequacy that IDsencounter when they try to use CAD tools [START_REF] Tovey | Concept design CAD for the automotive industry[END_REF][START_REF] Dorta | The ideation gap: hybrid tools, design flow and practice[END_REF]. IDs tend to use tools that were not made for them and consequently struggle to maintain their creativity and be integrated into industrial processes. Hence,it is difficult to fully understand the specificities of ID CAD compared with engineering CAD and graphical CAD.Moreover, it is unclear how these different tools might be made compatible.

The second motivation for this paper relates to design science and design theory.Recent advances in design theory provide us with an ecology of theories that might be powerful enough to bridge the gap between different professional approaches to design (Le Masson et al. 2013). However, research on CAD tools very rarely buildsanalytical framework on design theory.Many research works actually use more generic notions, such as -boundary objects‖ or -artifacts,‖ which are inherited from sociology or management, that tend to hide the specificities of design reasoning and barely account for the variety of CAD tools and the incompatibilities that were recorded in the use of these tools by professionals.

Given these two motivations, this paper aims to account for the design logic at the root of CAD tools used by engineers, 3Dartists, and IDs by using design theoryto model the reasoning steps of designers using these tools. More precisely, this paper intends to understand the specificities of ID CAD in comparison with engineering CAD and 3Dartist CAD.

To summarize, this paper clarifies: (1) Thedifferences in the missions of professional CAD tools: engineering CAD supports the design of product models so that they are compatible with a -physical‖ environment and generic conditions; 3Dartist CAD tools support the design of a single object to be included in a -virtual‖ world;and ID CAD tools support the design of a singularity for genericity-that is, a singular original style to be applied in generic conditions.

(2) The design logic behind each professional CAD tool: engineering CAD relies on modeling, that is, finding a parametric product model by combining existing design parameters (DPs) to address existing functional requirements (FRs). 3Dartist CAD relies on the immediate design of the object, similar to sculpting or making art more generally.It directly creates the virtual object and is not a -representation‖ of something that would exist somewhere else. Instead, it is a -presentation‖-the object is -made present‖by the 3D artist using CAD. Finally, ID CAD aims at designing styles models, which is very specific and different from modeling (i.e., fitting a general model to a particular environment) and art making (which does not necessarily require models).

We start by identifying the tendencies of the literature when analyzing such tools. We formulate a generic framework to model the reasoning of CAD tools based on design theories. We then use our framework to analyze the following:(1) how it accounts for the differences between contemporary professional CADs (synchronic approach);and (2) how it accounts for the long-term evolution of professional CAD software (diachronic approach).

Literature review

The literature clearly distinguishes between threegroups of professionals whouse CAD tools: (1) engineers who work in the manufacturing industry and use CAD tools to design industrially produced physical objects; (2) 3D artists who work in the entertainment industry and use CAD tools to design virtual environments and content for animation, movies, and video games; and (3) IDs who work in industry and concentrate on the user experience of manufactured products. For each of these groups, the literature in computer science, engineering design, and design creativity is distributed along the following two axes:(1) the modeling capacities of the geometric kernels, which define what type of objects can be created; and (2) the tools' interfaces, that is, man-machine interfaces (MMI).

CAD tools for engineers

The first identified category in CAD tool literature isengineering CAD tools, such as SOLIDWORKS, Pro/ENGINEER, AutoCAD, and NX. Over 20 years ago, a special issue of Research in Engineering Design [START_REF] Rosen | Special issue: Advances in representation and reasoning for mechanical CAD[END_REF] underlined the paradigm shift in CAD from drafting to product data modeling. It proposed hypotheses for the future of engineering CAD modeling based on the emergence and potential generalization of -features‖ in CAD [START_REF] Rosen | Feature-based design: Four hypotheses for future CAD systems[END_REF]. According to these hypotheses, a common set of subfeature element types, elementelement relations types (spatial, logical, etc.),and design features associated to the subfeatures and relations can:enable performance, cost, and other lifecycle analyses; embody physical principles; and enable checks for consistency with design principles. For example, [START_REF] Shah | Assembly modeling as an extension of feature-based design[END_REF] developed concepts for product modeling with a uniform set of structures and relationships, and developed approaches to derive the assembly location from high-level specifications. It appeared that no single feature set could satisfy all engineers, so the -features‖ used in modern CAD are only a limited approximation of the CAD tools based on a featurebased representation as imagined by Rosen et al. 1 Retrospectively, it appears that this special issue was quite visionary in two aspects:

(1) It insisted on the modeling aspect of CAD, where a CAD tool finds a model (for example, of an object, parts, components) that can be considered as -satisfying‖ the composition of -features‖ to meet requirements. (2) It identified a trend in CAD in that the design of new relations was not limited to geometric relations, as in parameterized drafting, but could be extended to relations between several types of entities and, in particular, functional entities.

This was confirmed by subsequent research: for a summary, see [START_REF] Zeng | Fundamentals of next generation CAD/E systems[END_REF]. For instance,works on CAD modeling aim to integrate conceptual design [START_REF] Brunetti | A feature-based approach towards an integrated product model including conceptual design information[END_REF]; extend parametric design to complex products,such as cars [START_REF] Salehi | Development and Application of an Integrated Approach for Parametric Associative CAD Design in an Industrial Context[END_REF]; support constraint identification for more efficient optimization logic [START_REF] Bettig | Derivation of a standard set of geometric constraints for parametric modeling and data exchange[END_REF];enable modeling with heterogeneous solids (Liu et al. 2004a); work on a language of part modeling to enable higher compatibility (Xu et al. 2013); or create multi-level assembly models for CAD [START_REF] Chen | Multi-level assembly model for top-down design of mechanical products[END_REF]. This modeling logic structures the computer science literature on engineering CAD, which is oriented toward improving the geometric model kernel and interfaces of the tools.

Geometric model kernel forengineering CAD tools

The geometric model kernel is the engine of the CAD tool. It determines what type of objects can be modeled and managed by the software during the design process. This category of the literature is globally evolving toward more functions and the ability to solve more problems of various natures, while being able to handle new classes of objects. It takes into account cognitive efforts of designers [START_REF] Nguyen | A physiological study of relationship between designer's mental effort and mental stress during conceptual design[END_REF]. As shown in [START_REF] Liu | A fuzzy psychophysiological approach to enable the understanding of an engineer's affect status during CAD activities[END_REF], CAD systems aim to -recognize, interpret and process human emotions‖ to integrate the potential bias that can arisein the process of designing a concept that is -right first time.‖ Some scholars, such as [START_REF] Mandil | Geometrical tools for the description and control of functional specifications at the conceptual design phase[END_REF],modify the geometric kernels to describe new attributes, such as geometric dots and line segments, to depict early design-stage mechanisms. [START_REF] Dyn | Four-point curve subdivision based on iterated chordal and centripetal parameterizations[END_REF]proposed replacing uniform parameter values by chordal and centripetal values to achieve nonlinear schemes that are invariant under solid body and isotropic scaling transformations. These papers have shown the progressive implementation of capacities for the modeler to handle more types of objects, such as functional specifications depicted geometrically. The functions and capacities of the software are also affected by the ability to manage more constraints, some of them of a different and totally new type, such as user preferences [START_REF] Kelly | Incorporating user shape preference in engineering design optimisation[END_REF]. CAD can even be used to -automate the procedure of customization‖ while using standardized components [START_REF] Kwok | Shape optimization for human-centric products with standardized components[END_REF].Because of increasing data and knowledge generated during the design and manufacturing processes, [START_REF] Ouertani | Traceability and management of dispersed product knowledge during design and manufacturing[END_REF][START_REF] Bodein | Decisional model for KBE implementation in a commercial CAD software[END_REF]proposed a new framework for the exploitation and curation of knowledge. [START_REF] Goel | Cognitive, collaborative, conceptual and creative -Four characteristics of the next generation of knowledge-based CAD systems: A study in biologically inspired design[END_REF])summarized these trends by stating that future CAD should be -cognitive, collaborative, conceptual and creative,‖ where -creative design‖ is actually a capacity to access -systems functionally and at different levels of abstraction,‖ remaining in a -search‖ paradigm where the designer looks for solutions to a given problem (p. 897).

Interfaces for manipulating digital engineered content

Interfaces enable interaction with machines. The growing demand for experiencing products at the early stages of design has created a strong need for new interfaces with extended sensory-motor capacities. There is a progressive shift from old interfaces, such as the mouse and keyboard, toward immersive ways of interacting, such as touch, multi-touch, and virtual reality, to propose enriched interactions [START_REF] Stergiopoulos | Design of a 2-finger hand exoskeleton for VR grasping simulation[END_REF][START_REF] Deschênes | An unified approach for a simultaneous and cooperative estimation of defocus blur and spatial shifts[END_REF]. [START_REF] Kang | Feature-based 3D CAD modeling on smart device using multi-touch gesture[END_REF]focused on the step of transferring contentto new portable devices, that is, tablets and smartphones with multi-touch. (Liu et al. 2004b)proposed a system for direct interaction and modification with a haptic device (see also [START_REF] Fuge | Conceptual design and modification of freeform surfaces using dual shape representations in augmented reality environments[END_REF].

To summarize, publishedpapers on CAD tools for engineers seek to increase the capacities of geometric modeling kernels to handle more functions, algorithms, and properties of the underlying design concept throughout the entire design process,which includes the factory's design, manufacturing, and maintenance. The digital object tends to become the most perfect model of the future real product, up to the chosen tolerances. Furthermore, the literature aims to increase interactions between the user and model, for example, with immersive technologies.

CAD tools for 3D artists

The second identified category in the literature is artistic CAD design tools, such as 3ds Max, Maya, and ZBrush. 3D artists produce 3D models required for video games, animated films, and special effects in movies, known as computer-generated imagery (CGI). This family of products evolves within a galaxy of other services, such as animation, rigging, texture mapping, unfolding, and rendering. The literature again stresses two aspects: the geometric model kernels and the interfaces for manipulating them.

Geometric model kernel of artistic CAD tools

The geometric model kernel for artistic CAD tools is usually designed to manage the highest number of polygons. The more polygons, the greater the density of detail that can be achieved.In most cases, artists need tools that allow the direct manipulation of the rendering result. The most advanced technique in this domain is generically called voxel, and pixolin ZBrushterminology. New models have been introduced to address the specific needs of the entertainment industry, such as video gaming, which often encounters the issue of computing collisions inside real-time environments [START_REF] Mishkinis | Approximate convex hull of affine iterated function system attractors[END_REF]. [START_REF] Loop | Approximating Catmull-Clark subdivision surfaces with bicubic patches[END_REF][START_REF] Loop | Approximating subdivision surfaces with Gregory patches for hardware tessellation[END_REF]introduced a new method of approximating subdivision surfaces,which are the most used modeling technique of 3D artistic CAD tools, with hardware accelerated parametric patches, which improve the memory bandwidth requirements for patch control points. This allows an extension of the number of polygons displayed by the computer to add more detail to the model. [START_REF] Kowalski | Art-based rendering of fur, grass, and trees[END_REF]proposed building on the ability of artists and illustrators to evoke the complexity of fur or vegetation with relatively few strokes on the boundaries of objects. This reduces the total number of polygons while increasing the richness and density of detail. Walt Disney Studios recently published the process it used for its Oscar-winning animated short filmPapermanin 2012.In their SIGGRAPH talk, Whited et al. [START_REF] Whited | Computer-assisted animation of line and paint in Disney's Paperman[END_REF]) explainedhow a hand-drawn appearance can be achieved with computer-generated models to make final animated movies look similar to old animated movies that were drawn by hand.

Interfaces for manipulating artistic digital content

Software designers and researchers have proposed new types of interfaces specially designed for 3D artists. The most visible strategies are the imitations of the sketch and clay modeling designing steps. For example, as early as 1996, [START_REF] Gross | Ambiguous intentions: a paper-like interface for creative design[END_REF]proposed a system that could recognize and interpret drawings. [START_REF] Igarashi | Teddy: a sketching interface for 3D freeform design[END_REF][START_REF] Nealen | FiberMesh: designing freeform surfaces with 3D curves[END_REF]) worked on a project for creating 3D shapes from sketched two-dimensional (2D) input. This technique allows the user to add, remove, and deform control curves, which then generate free-form surfaces. The curves can have arbitrary topologies and do not need to be connected to one another, which allowsthe system to manage both curve deformation and the subsequent surface optimization. Other researchers, such as [START_REF] Keefe | CavePainting: a fully immersive 3D artistic medium and interactive experience[END_REF],have explained how new 3D immersive interfaces can be used to generate artistic 3D content. They proposed an artistic medium that uses a 3D analog of 2D brush strokes to create 3D works of art in a fully immersive environment. [START_REF] Zhang | Virtual clay modeling system with 6-DOF haptic feedback[END_REF])proposed a virtual clay modeling system by which users can directly manipulate the shape of a virtual object as they can do with a clay model.

In papers on CAD tools for 3D artists, researchers havesought methods that increase the capacities of geometric modeling kernels to optimize real-time and recalculated visualization with the best resolution possible. This focus is required because the design exists and evolvesinside a virtual environment for which it must be optimized. Designers want to make the model plausible inside its environment. The profusion of details creates a backstory, past, and context. Conversely, the literature proposes interactions with rich interfacesthat have a strong focus on sketch-based interfaces and clay modeling metaphors.They imitate the artist's studio and ancient techniques. Natural and direct interfaces are intended to help the designer control an appearance and a final rendering result so that the model can blend within the virtual environment.

This first review shows how similar issues-such as modeling kernels and interfacesare addressed differently by the literature when considering engineering CAD or artistic CAD tools. We now provide an example of such a dichotomy with the issue of textures.

2.3Textures

Engineering CAD and artistic CAD tools require an appropriate rendering of the 3Ddesigned product inside its environment, but for different purposes. Engineers require good rendering engines and libraries of materials to assess the object. Engineering CAD tools integrate a library of materials with properties as close to the real materials as possible. [START_REF] Choi | A multi-material virtual prototyping system[END_REF]proposed upgrading the fit between the model and the real product, once manufactured. Engineering CAD tools integrate libraries of industrial materials with properties such as color, stiffness, and weight, and take into account these properties for the entire object, for example, the effect of surface material stiffness and surface material weight on the entire stiffness and weight.

3D artists need to assessthe future aesthetic properties of the future virtual product inside its virtual environment. [START_REF] Lasram | Procedural texture preview[END_REF]proposed a new algorithm to simultaneously optimize the quality and rendering speed for procedural textures, and for their control and parameterization. Artistic CAD tools integrate libraries of natural appearances, such as skin, trees, fur,and sketch strokes, in addition to libraries of -virtual‖ appearances in areas such as fantasy, science fiction, and cartoons.

Thus, we can characterize two contrasting CAD families. Both have a requirement to -design a new artifact in a digital environment,‖ but have the same apparent issues regarding the computing engine and MMIin a similar way to any software, such as statistics software, office software, or enterprise resource planning. The literature helps to characterize some differences. The action logic is different: it ismodeling in the case of engineering CAD and designing one single artifact in the case of3D artist CAD. Hence, the issues with the computing engine are different: they are to increase model fidelity in engineering CAD and increase singularity and details in 3D artist CAD. Additionally, the MMI issues are also different: in engineering CAD,a MMI tends to increase the number of available features and combinations and the capacity to fit into multiple environments, such asa factory, logistics, retail, andwith end-users, whereas in3D artist CAD, MMI attempts to enrich the virtual environment, the artifact rendering, and the fit between the virtual environment and the artifact itself.

2.4CAD tools for ID

The questions are why and how ID CAD should be different and not simply a personalization or hybrid of the two types we have already identified. [START_REF] Tovey | Styling and design: intuition and analysis in industrial design[END_REF]explained the precise differences between the needs of IDs and their engineer colleagues. According to Tovey, IDs have the dual needto have tools for working on the aesthetic properties of products and their meaning,and to integrate with industrial firms and therefore work with 3D models intended for use in manufacturing objects,in the same way as engineers. [START_REF] Fuge | Conceptual design and modification of freeform surfaces using dual shape representations in augmented reality environments[END_REF])confirmed this dual need. On the issue of -shape design‖, IDs require a tool that has -to provide designers with the maximum flexibility in exploring a variety of shapes‖ and simultaneously to provide a -representation of the underlying surface.The authors finally proposed a direction for a renewed family of tools based on sketching and clay modeling techniques transposed into CAD environments [START_REF] Tovey | Concept design CAD for the automotive industry[END_REF].

Similarly, [START_REF] Bae | ILoveSketch: As-natural-as-possible sketching system for creating 3D curve models[END_REF] proposed ILoveSketchsoftware, which encourages IDs to express themselves with glyphs and pen-paper metaphors. This project is an attempt to introduce within a virtual environment animitation of the traditional sketching process. [START_REF] Thurgood | Use of 3D non-contact digitisation and 3D touch modelling systems within automotive seating design[END_REF]used immersive interfaces to create services close to clay modeling, similar to those used by 3D artists. However, transferring from a CAD model to another type of data requires large computational efforts and breaking the link to the source file, where the design tree and all the design features are stored, to obtain what is called a -dead skin.‖ Another model conversion will be required if the designed prototype is validated.Thus, adding -free-form‖ modules to engineering CAD does not solve the issue of the compatibility with engineering CAD logic.

Finally, the literature on ID CAD tools underlines the mismatch between the needs of IDs and the digital tools they can access. Even with tuned-up engineering environments with specific interfaces, IDs still lack the capacity to express themselves freely because of the specific modeler kernels. Althoughcreative prototypes have been proposed, the models they generate can be integrated into industrial environments only after data conversions [START_REF] Thurgood | Use of 3D non-contact digitisation and 3D touch modelling systems within automotive seating design[END_REF] that involve heavy losses of information. These data conversions are called the "designgap" [START_REF] Tovey | Concept design CAD for the automotive industry[END_REF][START_REF] Dorta | The ideation gap: hybrid tools, design flow and practice[END_REF]. After more than 15 years of development, very few of these tools are used by IDs on a daily basis.

The challenge of making simple modifications to existing families of CAD tools to meet the needs of IDs appears impossible to solve. IDs lack dedicated tools that can address their specific reasoning and design processes while integrating them into industrial environments. Over the 15 years that have passed sincethe first papers on the use of CAD in industrial design, IDs are still struggling inside companies to find the right tools, to express themselves,and to communicate with other designers and fully participate in the entire design process.

Research question

This literature review helps to reject two common but too-simple hypotheses regarding ID CAD tools.CAD tools for IDs cannot be adapted from engineering CAD tools and CAD tools for IDs cannot be adapted from 3D artist CAD tools. This results in theresearch question: what is the specific design logic of IDCAD? As seen with engineering CAD and 3D artist CAD, CAD software is coherent with the design action logic of the user.2 One uses CAD to create -a new artifact in a digital environment,‖and the literature helped us to clarify the meaning of -new‖ and -artifact‖ in each case. -New‖ for engineering CAD means a new combination of known features, whereas -new‖ for 3D artist CAD means an original single digital object. In engineering CAD, the user designs a model of the future product, whereas in 3D artist CAD, the user directly designs the final digital object. In ID CAD, it remains for us to determine the meaning of -artifact‖' and -new.‖

Method

Analytical framework

To differentiate between the families of CAD software, we rely on recent findings in design theory that allow a better characterization of the specificities of design processes and the CAD tools mobilized for them. Recent advances in design theory help to characterize an ontology of design [START_REF] Hatchuel | Towards an ontology of design: lessons from C-K Design theory and Forcing[END_REF]Hatchuel et al. 2011a):

(1) Design involvesmanaging the unknown. In design, there is a language of the unknown (Le [START_REF] Masson | Design theories as languages for the unknown: insights from the German roots of systematic design (1840-1960)[END_REF]. Design is a situated activity that implies the manipulation of knowledge about the known and concepts, which are the management of the unknown [START_REF] Hatchuel | C-K design theory: an advanced formulation[END_REF].

(2) Design is a generative process. It allows the progressive creation of new objects, values, products, uses, or technologies, and the creation of new knowledge, which may or may not be related to the final artifact. (3) Design theories offer a characterization of the evolution between the known and the unknown. From the known, it is possible to organize the unknown, and the explorations of the unknown can generate new knowledge. (4) The performance of the design is, very generally, 2D: generativity of the design (is it new, original, etc.) and robustness (feasibility, domain of validity, etc.). These results help us to build an analytical framework for CAD. CAD is a media to help move from one known-unknown estate to another through a generative process. We need a way to characterize the known and unknown. Many theories provide models for the structure of the known and unknown in design(Le [START_REF] Masson | Design theories as languages for the unknown: insights from the German roots of systematic design (1840-1960)[END_REF]Hatchuel et al. 2011a). For this paper, we rely on classical language: DPs, FRs, and their relationships. This language, or a variant of it,can be found in many formal theories,such as general design theory [START_REF] Yoshikawa | General Design Theory and a CAD System[END_REF], axiomatic design [START_REF] Suh | Principles of Design[END_REF],and the coupled design process [START_REF] Braha | Topologial structures for modelling engineering design processes[END_REF]. Zeng and Gu showed that this language of DPs and FRs could be useful for describing the design process and evolution of the artifacts in the design process (Zeng and Gu 1999a, b). DPs are the means of action of the designers;that is, these are what they can choose or parameterize, and where degrees of freedom exist. For example, DPs can be a form factor, dimension, material, or specific painting technique. FRsare the design targets of the designer. FRsare used to describe the expected performance of the design. They can be a tolerance, mass, dimension, specific meaning, or style. The design process is characterized by the progressive exploration of the unknown and the expansion of the known. In FR-DP language, for instance, at the beginning of the design process, some FRscan be known, but how to obtainitis unknown, even if some potential DPsareknown. Hence, the relationship between FRs and DPs is partly unknown. 3 In the end of the process, one knows how to obtain the FRswith the known DPs.Moreover, often the relationship between FRs and DPs might take the form of a rule that has a certain domain of validity, so that at the end of the design process, one can actually design the entire object in the validity domain.

This simple framework helps us to characterize the design process steps, according to Table 1.

Table 1.Framework to analyze a CAD design process.

Category of CAD tool

Inputs

Outputs Criteria of success of the considered design step DP: known/unknown FR: known/unknown Relationships between DP and FR: known/unknown DP: known/unknown FR: known/unknown Relationships between them: known/unknown Note: For each CAD tool, one characterizesknowns and unknowns at an initial stage and knowns and unknowns and the final stage, and characterizes the type of performance that is targeted during the process.

The language of DPs, FRs, and their relationships helps us to characterize many design situations. For instance:(1) in engineering design, at the starting point, FRs are provided, but not the DPs to achieve them; (2) in industrial design, a brief is provided as a starting point andis a fuzzy FR (e.g., -a smart shopping cart,‖ see for instance Hatchuel et al. 2011b), and the design process progressively enriches the FR, for example,designinga new FR that can be associated to a smart shopping cart;and (3) in machine design, there are often many FRs given by the customer and many DPs to be used to address these FR (available processes, available material, etc.), but the relationship between the given FRs and the given DPs is partly unknown.

Our framework helps us to address our research question by characterizing the design situations to which each CAD tool is adapted.We proceed in two phases:

(1) We first conduct an experimental comparison to characterize the design logic of CAD tools.

(2) We then show that this design logic helps usto explain general trends in the development of CAD tools. In the following, we provide detailed methods for each phase.

Case study

Our experiment is based on the design of a new motorbike tank. The general brief was to design a -dynamic, muscular‖ tank.This was then evolved into three design briefs, each of which was adapted to be managed by the professional using particular CAD software. This product was chosen because it could be designed by any of the three categories of professionals. It exhibits technical, style, use, and aesthetic constraints.

This design exercise was applied to three specific CAD tools that are considered archetypal by designers and used by professionals on a daily basis:

(1) The use case for the engineering CAD tool was implemented using SOLIDWORKS software. This CAD tool was developed for engineers working in various industries, such as robotics and musical instruments. It is based on the paradigm of procedural modeling.

It is connected with many -workshops‖ for design analysis, such as resistance, weight measurement, and mechanical animation.

(2) The use case forthe artistic CAD tool was implemented using ZBrushsoftware. This CAD tool was developed for 3D artists working in entertainment. It is specialized for the precise modeling of biological materials and original objects for virtual environments. It is based on the paradigm of clay modeling and connected with many -workshops,‖ such as rigging foranimation and deformations, and rendering. (3) The use case for the ID CAD tool was implemented using CATIA Imagine &Shape software. This workshop was developed,with IDs involvement,for IDs working on the form and aesthetics of products in several industries. It is specialized for the modeling of qualitative shapes and draws from the entire CATIA environment. It is connected with many -workshops‖ suited for every step of the design process and most of the types of technical expertise (e.g., mechanics, electrics, and hydraulics), from ideation to design refinement and production. As mentioned above, very few CAD tools meet IDs' expectations;however, previous experiments have shown that the CATIA Imagine &Shape kernel, interface, and integration have specific capacities that make itamong the very few CAD tools that meet at least some IDs' expectations [START_REF] Arrighi | Addressing constraints creatively: how new design software helps solve the dilemma of originality and feasibility[END_REF]. Regarding the professionals, we had to avoid bias resulting from the user's personality and education. Our issue was the comparison of the CAD tools and not the comparison of the professional users themselves. To avoid this type of bias and to focus on the comparison issue, we had to control the designer using the CAD software. Ideally, we needed the -same‖ professional user (same personality, tastes, etc.), but someone who was capable of using engineering,3D graphic, and ID CADs with comparable and high capacity. We had the opportunity to rely on one such -ideal‖ participant.We identifieda professional designer that was educated in all three professions and capable of using all three software systems. Thus, in this experimental study, we could compare the different software systems andminimize the bias introduced by different users. Note that there is no statistical relevance in the comparison, but analytically, we ensure that the differences we see are a result of different software systems used by this particular user and not the result of different users. We could not identify all the differences between the CAD software systems, but the differences we do identify can be attributed to those systems.

Because the same user conducted the three exercises, there might be a form of learning involved. This form of learning was maximized: the user performed the tasks in parallel, beginning with one CAD software system, then movingto another, and returning to the initial system. In fact, the designer worked in this way to be betterable to determine the differences between the three software systems. The experiment enabledthe designer to characterize the differences between all three systems.

During the process and at the end, the designer was interviewed.The designercontributed to the comparison and differentiation of the three processes and three resultsthat followed the analytical framework in Table 1.

Historical perspective

In the first phase, we characterized the design logic of CAD tools. This result was obtained with a specific use case and software systems. To generalize this result, in a second step, we validatedour findings with a study of the historical developments of the CAD software systems. Relying on specific milestones in the development of the precursors of the cutting-edge contemporary software tools,we trackedhowthese specific categories of tools have evolved over time.

We conducteda historical analysis on each of the three software families:engineering design tools;graphic art tools, which included, for these broad categories, tools from 2D graphic creation to 3D animation tools and technologies; and industrial design tools.

Results

Design logic of CAD tools for engineers, 3D artists, and IDs

Designing with an engineering CAD tool

In the case of designing a -dynamic, muscular tank‖ using engineering CAD, the designer could not begin with the general brief. First, he had to translate it into known FRs. He explained that he considered that the tank had to achieve a specific volume, weight, and stiffness properties. He also took into account that the motorcycle tank would be manufactured and assembled;thus, it would have to encounter real-world constraints, such as rain, sun, and gravity, and would have to be compatible with norms, rules, and legal obligations. Regarding DPs, the designer relied on a set of materials and manufacturing processes that are available in the engineering CAD library. Thus,before using CAD, the DPs and FRs were fixed.

During the design process, the engineer configured a pre-established and mandatory set of DPs to achieve known FRs. The engineer used commands and functions step by step to construct the virtual mock-up, and by doing this generated what is known as a design tree. The design tree contained the functions and parameters, and the relationships among the different geometric entities. For instance, the designer specified certain dimensions of the tank to meet the volume criteria.The design tree also specified certainthickness parameters, for example, the position of ribs, to ensure the stiffness criteria (see Figure 1). A single product was not designed; instead,a parameterized and reconfigurable base of rules were produced that could generate a family of products.The result of the design in engineering CAD wasnot a single product but rather an algebra of rules. This algebra of rules defines how the components are spatially positioned,in addition to the links between them, the functions, and their parameters. This algebra can be mapped to an infinity of solutions. The engineer guaranteed that the set of created rules was robust to variations in DPs (e.g., different materials or manufacturing methods) or even FRs (e.g., modified volume requirements or a new legal regulation created during the design process).Clearly, the designer could use irrelevant parameters so that the CAD tool allows parametric variations, but these variations are poorly related to important topological variations. Digital engineeringappears to be a design process of generalization.The artifact is one representation of a -genre,‖ that is, it helps to address -generic variety.‖ The product is robust to changes in its DPs (components, dimensions, etc.) and its FRs (environment, etc.)one simple illustration of this is the logic of tolerances in engineering design.

Designing with an artistic CAD tool

Using 3D artist CAD, the designerbegan with a brief for a -dynamic, muscular tank‖. The designer noted that the design brief for the artistic 3D profession could also be a 2D sketch or illustration. The initial sketch providedindications ofthe environment and the object tobe designed-the motorbike on which the tank would be installed, the environment into which the motorbike would be inserted, and so on.The designer then extendedthese elementsso the artifact created was unique. The motorbike would never be manufactured; it stayed inside a virtual, controlled environment.

To obtain a muscular tank, the designer exaggerated the muscular aspect of his design; he added extra refinements and features.To address the FR -dynamic and strong,‖ he thought of a 5year-old motorcycle that was used in the desert, and generated a specific DP: -there are impacts on the front lens, the paint is worn off and decolorized.‖ This motorbike wasmade specifically for a video game and driven by a specific character in a special environment, under specific lighting, and with a detailed paint job, including the detail ofa specific little scratch on the side caused by a collision. This list of FRs was addressed by a combination of DPs: the driver, joints between the surfaces, number on the side, and color of the paint.

At the beginning, the designer thenhad a collection of DPs and FRs. He freely manipulated the DPs and FRs, adding some and suppressing others, under the guidance of an artistic director. Unlike his approach to the engineering experiment, he did not generate a generic relationship between DPs and FRs with a large validity domain. He created a unique correspondence between a list of new DPs and new FRs, with the longest list possible that includedmany -details.‖ Each detail had to convey meaning and intention to animate the virtual object.

Digital artistic design is a design process of congruence with the initial list, that is, the verbal brief or 2D sketched example, and extension,which adds a profusion of details to obtain a unique artifact, that is, to achieve a form of singularity.

Designing with an ID CAD tool

Using the ID CAD tool, the designer began with a -dynamic and muscular tank,‖ but he also added other elements, such as global dimensions, the process of fabrication, and manufacturing cost. The designer beganwith references, such as sketches, pictures, or photos. Similar to the engineering CAD experiment, the designer took into account that the tank would have to encounter real-world constraints, such as rain, sun, and gravity, and that it must be compatible with norms, rules, and legal obligations. Simultaneously, it had to satisfy specific usage and aesthetic constraints that were difficult to measure.

The design process required the creation of details. For the first step, the designer explored a high density of details in a similar way to a3D artist working with CAD tools. For the second step, the designer omittedsome details to fit into a small set of parameters in the data format of a manufacturable file, thereby creating a conceptual modelfor the tank very similar to the type of files produced by engineering CAD.

This conceptual model synthesized and simplifieda large variety of DPs, such as points, lines, curves, surfaces, and their parameters,into a smaller set that wascompatible with the constraints of engineering design and manufacturing. This limited set was intended to convey the dynamism and muscularity of the tank. In our case (see Figure 3), the conceptual model is the instruction about the character lines of the tank that make it dynamic and muscular, in addition to how the character lines respect the surface quality: their position, thickness, orientation, style, and artistic influences. Software requires the ability to extend the list of DPs and FRsand synthesize the explorations into a conceptual model.

In the analytical framework (see Table 2), the design process generates new DPs and FRs and it also generates new relationships between these DPs and FRs.This process creates a new algebra that can be activated and parameterized on demand once characterized.

In the case of ID CAD, the result is not only the particular shape obtained but also the conceptual model that underlies this particular shape,that is,it helps to create this shape but also a family of shapes sharing a common character. Hence, it possesses some of the properties of engineering CAD (i.e., model and genericity) and some of artistic CAD (i.e., generation of FRs and DPs, and singularity). The capacity to create conceptual models makes this type of tool suited for what we call generic singularity. The artifact designed by the ID is a specific configuration of his conceptual model.

There is the question ofwhat is -new‖ in this process.Similar to his role as a 3D artist, when working as an ID, the designerused CAD to express himself freely to create an original artifact. But he also had to take into account the constraints of the development of the real object (development, production, retail, marketing, etc.). Newness is then defined as the capacity to make an original model and not only a single digital tank under the industrial constraints. Ideally, this model would be valid not only for the tank of the motorbike, but also it might be a model of -muscularity‖ that would be valid for a large set of objects, for example, the tank, wheels, helmet, and motorcyclist'sjacket.The performance of the designer using ID CAD creates a conceptual model that is valid on the largest domain possible.

Finally,there is the question ofwhat comprises a conceptual model is that is new and valid for a large set of objects. This corresponds to what is usually called a -style,‖ for example, the style of an artist or time period. We finally determine a deep and critical identity feature of an ID: an ID creates a personal style or the style of the age. Additionally, this style corresponds to a new but stabilized, constant relationship between new or old DPs and new or old FRs.Whilethe 3D artist creates a singular object with CAD and the engineer creates a generic variety of objects with CAD, an ID creates a generic singularity by creating a new style, which is a new conceptual model. After completing the analysis based on the use cases of archetypal tools, we can characterize, from a design perspective, the differences among the categories of CAD tools and why they are suited to their specific design users.

Conclusions on the archetypal CAD design tools

 Engineering CAD tools seek to generate the best possible algebra of rules between the prescribed FRs and DPs. This algebra must be valid on a domain of DPs and FRs; the wider and more robust this domain, the better.Thus, there is a logic of genericity in engineering CAD.  Artistic CAD tools seek to generate the most detailed, refined,and unique list possible of coherent FRs and DPs.This list must be as long and as original as possible, in congruence with the prescription. There is no modeling logic;there isa logic of singularity.

 ID CAD tools can work with an incomplete set of DPs and FRs;they help to extend the list, creatinga sense of -muscularity‖ and DPs that can be associated with -muscularity‖ and they help create the associated conceptual model by linking DPs and FRs that are valid on a large validity domain,which can be referred to as a new style. There is a logic of generic singularity.

Historical evolution of CAD tools

We now verify whether this hypothesis is correct from a much wider perspective. There are many works on the history of CAD tools [START_REF] Arrighi | Lack of integration between engineering industrial design processes[END_REF] [START_REF] Fridenson | Inventeur salarié, automatisation et entreprise : expériences internationales, tensions et dynamiques[END_REF]. We rely only on some main milestones in each profession.

Evolution of engineering practices

We summarize the history of engineering CAD in Table 3. Engineering CAD was a technique to help to relate known FRs and known DPs,such as shape and material. The evolution is marked by the need to increase the list of available DPs and FRs, and the capacity to relate complex sets of DPs and FRs.

Evolution of 3D artist practices

The history of 3D artist CAD shows how 3D graphic CAD has beenprogressively open to be able to integrate denser details and new -types‖ of details. We summarize the steps in Table 4.

Evolution of ID CAD tools

For some time, there were very few dedicated tools for IDs.Despite this, the following challenges have progressively been overcome by some software systems for IDs:  translatingbetween the different data formats used by engineering design tools and industrial design tools;  representing objects with a very high surface quality, which is required especially to achieve high levels of precision in manufacturing;and  maintainingboth a holistic view of the object being designed and the ability to work in very local detail. In practice, this implies being able to realize modifications that need to be propagated only locally.

Finally,ID CAD tools support the creation of conceptual models (i.e., ID styles) in two ways:

(1) ID CAD tends to hybridize engineering CAD logic and 3D artist CAD in a two-step process: the designer first uses 3D artist CAD to have great freedom of exploration, which is possible with artistic CAD tools. For the second step, the ID uses engineering CAD to apply constraints. Some current software prototypes allow the designer to explore every dimension while designing and then the user activates constraints,such as the surface quality or process of manufacturing. (2) ID CAD provide a specific environment where IDs are aware of the constraints and are bound to make only models of a given surface quality,Hence with ID CAD, IDs can concentrate on the generation of the conceptual model and its originality becausethey have the guarantee that his model will fit the industrial manufacturing constraint. This corresponds to two strategies to generate a style with IDCAD: Strategy 1:maximal extension, then generation of a conceptual model. Strategy 2:modeling inside the constrained environment. The conceptual model is created by the embedded constraint inside the tool.

Conclusions on the historical study of CAD design tools

This historical analysis supports the previous findings (see Table 5):

(1) Engineering CAD relies on genericity: designers design a product, for mass production or one-offs, that have to fit into complex, real external conditions, such as users' behavior, robustness to external events, and conditions,and the trend consists of widening the set of rules to be managed with CAD. (2) For3D artist CAD tools, the DP are mainly graphic and the issue is to obtain denser and more precise shapeswhile addressing all the facets of an object in its environment to convey the meaning of the FR. CAD tools help to design and control as many dimensions as possible to obtain a unique and original design. (3) IDs, with both technical and artistic competencies, have been trapped between these two worlds until very recently. New ID CAD tools help at the present timeto address a large variety of FRs inside industrial environments and to have the capacity to generate new conceptual models, that is, to act in a "style making" logic. They combine the singularity of personal style with the genericity of a style applied to many different artifacts.

Discussion and conclusion

Characterization of CAD tools

We have characterized the underlying design processes of the CAD tools for three professions using our design theory model.

Engineering CAD tools

For engineering CAD tools, the design expansion is the making of a rule defining the relationship between DPs and FRs. The target for this class of designers is to ensure that the design fits within a variety of external conditions, that is,it will be generic for these conditions.The designers create a set of rules and not one single object. The global tendency of this type of software is the capacity to generate rules addressing more types of DPs and FRs, which implies more heterogeneous disciplines, and to validate them across wider and more precise domains. We call this tendency generic variety.

CAD tools for 3D artists

3D artists require the ability to expand the list of DPs and FRs. There are no rules and domains, only a unique result that must be as dense as possible in detail and meaning. The target is a singular and original realization. The global tendency of this type of software is to make more FRs achievable as a result of an increase in the number of DPs available. We call this tendency maximal singularity.

CAD tools for ID

IDs seek new and original DPs and FRs, and simultaneously try to generate new rules between those DPs and FRs. This process is different from engineering design because the rule is not the unique target: the DP and FR must also be formulated and generated. It is also different from 3D artist CAD tool design because the expansion of DPs and FRs is not sufficient: there is a need to converge on a stabilized relationship between DPs and FRs on a large validity domain. The target is to obtain a generic singularity, which is generic because the new rule is suitable on a validity domain anda singularity because it relies on new DPs and new FRs; it is the design of a new conceptual model, or a new style. ID uses CAD to obtain generic singularity.

5.2Perspectives

This work helps to explain CAD and, more specifically, CAD for ID, by relying on advances in design theory.

(1) It helps to clarify what is designed with CAD and to which of the design situations each is adapted.

(2) It shows that ID CAD has to be coherent with ID design logic, not the creation of a single artifact, but the creation of -the style of their age,‖ as claimed by Bauhaus, one of the most famous design schools(Le [START_REF] Masson | Design Theory at Bauhaus: teaching -splitting‖ knowledge[END_REF]. (3) Moreover, it helps to clarify two IDCAD logics: expansion and then selection, or expansion driven by constraint;that is,managing with constraints creatively. More generally, it appears that IDCAD confronts the critical issue of creating a style in software. This issue appears as new and critical for CAD: engineering CAD uses existing rules, DPs, and FRs to instantiate generic models (modeling logic), and the 3D artist actually designs a single artifact. IDCAD invents dimensions and also ensures that their creation has a large validity domain, that is, that the new -style‖ can be applied to a large set of -objects.‖

In further research, this effort to create models might be related to contemporary issues in other domains:

 Contemporary machine learning now extends beyond identifying known patterns and tends to use big data to discover unknown patterns [START_REF] Kazakçi | Conceptive artifical intelligence: insights from design theory[END_REF]. Hence, linking IDCAD and contemporary machine learning might be fruitful.Other areas of interest include IDCAD applied to big data issues or, conversely, machine learning algorithms applied to IDCAD.  IDs are not the only professionals to create models. Creative scientists also try to extend beyond the validation of hypotheses and aim at creating new theories for new hypotheses. Thus, software that helps to create models might be relevant to them. Thus, we have shown that the issue of IDCAD is far from being the orphan issue of one single profession; instead, it echoes the contemporary issues of science: invention of styleand model creation.

Figure1.

  Figure1. Four design steps of the engineering CAD tool, with finite element analysis (FEA) capability included: (a)sketching on 2D planes with a non-uniform rational basis spline; (b)general aspect of the final result; (c)stiffness simulation inside the tool, with FEA capability of the software system; and (d)volume and mass assessment inside the tool.

Figure2.

  Figure2.Six design steps of the 3D artist CADtool: (a)muscle reference, (b) import a low resolution primitive, (c)raw deformation of the low definition primitive, (d)sculpting the ribs at low definition, (e)sculpting additional ribs at high definition, and (f)final result with chrome material applied.

Figure3.

  Figure3.Six design steps of the ID CAD tools: (a)reference, (b)importing a primitive, (c)playing with the shape manipulators, (d)applying constraints over the manipulation cage, (e)editing the parameters of the rib, (f)final result inside an urban environment.

Table 2 .

 2 Characterization of the three archetypal CAD tools.

	Category of CAD	DP-input FR-input and	DP-output FR-output	Criteria of success of the
	tool	relationships between	andrelationships	considered design step
		them	between them
	Engineering	 Mandatory DP-input	 DP-output = DP-input	 Size of the domain
	(SOLIDWORKS)	 Mandatory FR-input	 FR-output = FR-input	 Degree of performance of
		 Partial relationships	 Robust domain of	the local optimums
		between known DP	solutions linking FR	 Robustness of the domain to
		and FR	and DP	both DP and FR
				modifications
	Artistic (ZBrush)  List of desired DP-	 New list of DPs, some	 Extension of the list
		input	similar to DP-input,	 Density of details
		 List of desired FR-	others different	 Unicity of the list
		input	 New list of FRs, some	 Superfluous DP responds to
		 List of imbricated	similar to FR-input,	superfluous FR giving the
		DP and FR that	othersdifferent	next designer the most
		describe a unique	 New list of imbricated	unique intention
		prescription	DP and FR with more	 Congruence between initial
			details and meaning	and final list
	Archetypal	 List of desired or	 New list of FR,	 Fabrication of the conceptual
	industrial design	mandatory DP-input	including mandatory	model
	(CATIA Imagine	 List of desired or	FR	 Robustness of the conceptual

Table 3 .

 3 Historical evolution of engineering CAD from the design theory point of view.

	Types of engineering	DPs	FRs	Issues
	CAD
	CADCAM (1970s, early	2D-draughting	Specific shapes to meet	Capacity to
	1980s)	Wire-frame and surface	product and process	automatically redesign
		modeling	requirements	Data compatible with
		Deformation modeling		computerized
		(Bezier logic, see		numerical

Table 4 .

 4 Historical evolution of 3D graphic CAD from the design theory point of view.

	Types of engineering	DPs	FRs
	CAD
	Wireframe (1960s)	Wireframe	Only contours
	Polygons (1960s)	Polygons: deformable	Surfaces; deformable,
		polygons, calculates	animated surfaces,
		reflection angles	Lighting
	Tessellation (1970s)	Tessellation and	Texture
		skinning
	Subdivision (1980s)	Subdivision techniques:	Smooth surface
		uniform basis-spline	rendering
		curves from artist's
		work
	"Clay modeling"	Voxel	Rich details on organic
	(1990s-2000s)		surfaces

Table 5 .

 5 Characterization of the three archetypal CAD tools.

	Category of CAD tool	Remarkable evolutions
	Engineering	Variety and number of DP and FR
		Complexity of the base of rules and their
		robustness
	Artistic	Variety and number of DP and FR
		Density and unicity of the combination of DP
		and FR
		Capacity to add an infinite number of relevant
		details when needed
	Industrial designer	Manage the -style making‖ logic, such as
		compatibility and rules

This is even ifengineering CADor

3Dartist CAD tools do not cover all facets of the action. For instance, engineering CAD tools support conceptual design quite poorly. In fact, future engineering CAD might try to address these design steps (see for instanceGoel et al. 2012, Zeng and[START_REF] Zeng | Fundamentals of next generation CAD/E systems[END_REF].

In some cases,such as adaptive/variant design, the designers already know a large part of the relationship between DPs and FRs and they use CAD to fix the final details of this relationship.


M Danner

Contribution of sociology to the analysis of the processes of "social closure"

come

Introduction

This research focuses on independent professionals in France. Workers in France are classified as independent professionals if they do not work as salaried employees or are self-employed. The labour market of independent professionals commonly includes two different kinds of professions: those that require specific conditions for access and those that are freely accessed. The former constitute a 'closed' labour market, whereas the latter make up a so-called 'open' labour market.

Survey methodology

Survey 1: the data provided by the INSEE job surveys helps to monitor a given population over the course of several years. For the purposes of this research, only first-time participants were surveyed over a period of three consecutive years (2003, 2004 and 2005), i.e. 169 886 subjects. Of these, 4274 worked as independent professionals.

Professions offering limited access include highly regulated sectors such as health care, the law and consultancy, which require specific State-recognized titles and qualifications. The length and cost of studies required to enter these professions explain why they are commonly practised by individuals from privileged socioeconomic backgrounds. Beyond the matter of legal closure, independent professions operating as closed labour markets are therefore also governed by a form of social closure (Weber, 1995). This particular feature of the labour market ensures certain privileges, such as the admiration of the profane, a degree of freedom and high levels of income.

In comparison with these highly regulated professions, access to other independent professions (such as agriculture, arts and crafts, business, artistic professions and other non-regulated professions) is relatively open [START_REF] Paradeise | Les professions comme marchés du travail fermés[END_REF]. These professions tend increasingly to require specific qualifications, but the level of these qualifications is still relatively low and may be compensated by a degree of professional experience. Qualifications in these professions are therefore not sine qua non conditions of access.

The table below provides a clear illustration of the contrast between open and closed labour markets in independent professions: 32% of independent workers in open markets have no qualifications at secondary level, as opposed to just 3% of independent workers operating on closed labour markets. In the case of workers with higher education qualifications, the proportions are respectively 15% and 89%. Because of the elitism that it implies and the absence of competition which it guarantees, the level of training required for accessing closed markets partly justifies the high levels of income within these professions. More than 50% of people working in these professions earn on average more than 15 000 € per annum, whereas workers in open markets earn significantly less -39% earn less than 10 000 € per annum.

More radically still, the proportion of individuals declaring high levels of income, i.e.

above 35 000 €, is significantly higher in closed markets (40%) than it is in open markets (7%).

The impact of 'social closure' on the artistic professions

Using this analytical framework, the case of the artistic professions require a specific examination: workers in this area, who tend to be socially and educationally privileged, share far more in common with workers in the regulated sectors of health care, the law and consultancy than with other non-regulated professions, as indicated by the table above. Unlike the case of regulated professions, however, the qualifications obtained in this area are not by any means a guarantee of effective employment. Qualifications are not a criterion of access or advancement in artistic professions, which rely more generally on reputation and integration within established networks that ensure visibility and recognition. The effect of informal advancement by successive integrations within networks connecting individuals, which ensures increased recognition, is a pyramidal structure with, at its summit, the 'winner-takes all markets', which enjoy high levels of income, and at its base, the imposing mass of anonymous and penniless artists (Frank et Cook, 1995). To this extent, it is not merely that professional recognition is not conditioned by qualifications in this particular market, since it is also the case that individuals with qualifications are not granted a legal monopoly in their occupation, which would help to protect anonymous artists from significant competition from amateurs, volunteers and other individuals who engage in the same activities as non-professionals.

However, although average income levels tend to be low despite high qualifications (see table 1), these artistic professions, let hope for considerably high profits. In addition, artistic professions, like all professions, enjoy nonetheless a degree of prestige in society that clearly sets them apart from other professions governed by open markets. The issues involved in closing these professions to any form of competition are thereby exacerbated.

To this extent, artistic professions constitute a fruitful object of study for the analysis of the informal exercise of social control over the process of market closure. A specific population, i.e. women, was selected to study this particular aspect of the issue. Since they now constitute the majority of students taking art subjects in schools and universities, women represent a genuine and potentially competitive work force in a profession that defined itself for centuries exclusively in terms of male thought patterns and forms of recognition.

Women represent only a third of independent professionals (32%). On the face of it, it may seem surprising to find so few women in the artistic professions (38%) despite the fact that so many women choose to study art-related subjects at secondary school and in higher education: at secondary level, women account for 79% of students opting for art-related optional subjects, and in higher education, subjects such as art, drama, architecture, dance and music are also heavily subscribed by female students. There are very few women in the artistic professions (painting: 37%, writing: 27%, music: 17%, film directing: 34%, singing: 47%, dancing: 68%), and even fewer with the status of author.

-The AGESSAthe organisation that manages social security issues for professional authors, including writers, authors and composers, and professionals in cinema, television, and photographynotes that just 31% of its affiliated author-artists are women.

-Likewise, the Maison des Artistes, which manages royalties for graphic and plastic artists, observe that just 40% of its members are women.

Processes of social closures affecting women

How might we account for this relatively low proportion of female authors in the artistic professions? This paper will consider three intimately connected and mutually reinforcing explanatory factors:

-The historical context; -The social context;

-Processes of self-selection.

In Antiquity, Aristotle distinguished the noble arts (the arts of language and numbers)

from the servile arts practised by slaves (such as painting, architecture, sculpture, instrumental music, but also agriculture, carpentry, pottery and weaving). In the Middle Ages, the distinction barely evolved, although artists and craftsmen began to constitute guilds. However, because of the strict regulation of the labour market by guilds and corporations, some workers became emancipated from these bonds by founding their own organisations or by soliciting the protection of a powerful patron.

In parallel, keen to increase his prestige and influence, the King founded the first Academies in the seventeenth century and granted a new status to artists who had chosen to operate independently of guilds and corporations. Artists in the Academies were intellectuals and scholars, and were drawn from the uppermost classes of the social hierarchy [START_REF] Darriulat | Introduction à la philosophie esthétique : De l'Académie au Salon[END_REF]. The realm of artistic creation thus underwent a first ideological conversion that ensured the social recognition of an intellectual activity that had been previously regarded as a manual occupation: creation was now construed as the production of essentially symbolic goods and the profession was no longer governed by necessity but became instead a vocation. In France, this ideology contributed to the elevation of the arts and to a distinct separation of artistic activities from the realm of manual labour [START_REF] Sapiro | La vocation artistique entre don et don de soi[END_REF].

These historical shifts in the profession were accompanied by cultural upheavals that did nothing to serve the interests of women. Women had always taken an active part in artistic activities. Since Antiquity, they had played musical instruments or created art works. In the Middle Ages, artists were still viewed as craftsmen and their corporations included both men and women, especially in music, weaving and embroidery. In convents, many women also contributed to the production of miniature illuminations and works of writing. Yet history has forgotten the names of the female artists who worked in the complete anonymity of workshops or who gave up their maiden name to adopt their husband's surname. Since the supports they used for their work were fragile materials, very few of their works have withstood the test of time.

The dark era of the fourteenth and fifteenth centuries was marked by the virulence of religious precepts and considerably diminished women's sphere of activity. In the Renaissance, because women tended to be excluded by the regulations of many guilds, traditional occupations were gradually reclaimed by men. In sixteenth-century

France, married women became legally incapable and the dominant view was that women should devote their lives to their children and their husband. The role of women as irreproachable mothers remained uncontested until the middle of the twentieth century.

Production constraints in agriculture, arts and crafts, and commerce enabled women to remain present on these markets to sustain activity, though it was men who commonly adopted the couple's professional identity (Battagliola, 2000). By contrast, the realm of artistic creation appealed more commonly to autonomous activities that involved the production of original work. This social position was difficult to maintain for women because it was a socially costly process for them to claim professional independence through the solitary exercise of an activity that was reserved exclusively for men and that was incompatible with their role as good wives and mothers (Heinich, 1993). Furthermore, painters and sculptors were not allowed to own a shop and to sell works other than their own in the name of disinterestedness and self-denial. Yet because they had little or no recognition on the art market, female artists struggled to earn a living from their work. Furthermore, the creation of the Academies, which had become sacred high places of artistic creation, did nothing to encourage women's access to these professions. Indeed, very few women were allowed to benefit from such training, unless they were from wealthy families or from a lineage of artists [START_REF] Sofio | La vocation comme subversion : artistes femmes et anti-académisme dans la France révolutionnaire[END_REF]. In other words, by elevating artistic activity into a liberal art, the professional realm was defined in parallel without the presence of women.

A historical approach to the issue provides crucial elements for understanding the conditions that governed the emergence and structure of professional realms, particularly the processes of closure determining the professional assertion of female artists. Forms of social closure in markets originating in the seventeenth century structured the field on a long-term basis, and so it was exclusively men who occupied the most prestigious and enviable positions. This partly explains why the functions of judge, art critic, producers, etc. were traditionally held by men proffering their judgements from the standpoint of a 'male sociodicy'. In other words, interactions between individuals were governed in such a way that they served to maintain an organized social order determined by gender differences that gave rise in particular to internal processes of professional segmentation. It has been demonstrated that in traditionally male-dominated professions which became gradually feminised though without being devalued as a result, women had neither the same functions nor the same status as men [START_REF] Repères Goffman | L'arrangement des sexes[END_REF].

Furthermore, beyond this historical and social context, common cultural representations have also served to shape conventional perceptions of artworks produced by women. With the first 'ideological conversion', the figure of the artist in popular belief emerged as a hypersensitive, tortured, illuminated and disavowed being standing before the crowds in the immensity of his solitude, in a state of self-denial, a

Christ-like figure serving as a sacrificial offering by way of elevating the community to enlightenment [START_REF] Heinich | L'Elite artiste. Excellence et singularité en régime démocratique[END_REF]. Yet this state of supernatural grace destined for a handful of elects was rarely bestowed upon women to the point of establishing them as charismatic leaders. Though often talented, women have only very rarely been represented as geniuses [START_REF] Nochlin | Why Have There Been No Great Women Artists?[END_REF]. By way of illustration, [START_REF] Brenot | Le génie et la folie, en peinture, musique et littérature[END_REF], who has addressed the close connection between genius and creative madness, includes just twenty or so women amid approximately 400 references in total. This minimalist conception of the creative potentialities of women remains a salient feature of our current cultural context and of the social representations of the quality of artworks by female artists [START_REF] Sofio | La vocation comme subversion : artistes femmes et anti-académisme dans la France révolutionnaire[END_REF]. Because they alone are able to access genius, men have acquired the right to delegate what Hughes calls the 'dirty works' to the rest of the (uninitiated) population [START_REF] Hughes | Professional and Career problems of sociology[END_REF]. Since they are barely recognized in elite circles, women are thereby compelled to choose between renouncing their practice or accepting subordinate or less prestigious positions such as salaried employment.

From selection to self-selection

A second survey, relating this time to qualified workers, was carried out in order to extend this theoretical analysis and to provide evidence for the claim that female artists tend to withdraw from the most prestigious careers in the arts. Despite their specialised qualifications, women are more likely to be unemployed than men (45% as opposed to 34% of men). Furthermore, if they have secured employment, female workers are less frequently positioned in managerial positions or in intellectual professions (respectively 16% and 30%), and women trained in these areas are fewer in numbers in occupations relating to information, the arts and the performing arts (respectively 6% and 15%). Of those women who had secured jobs in these areas, just 8% stated that they worked in an artistic or journalistic profession as an author (painting, writing, music, acting, dancing...) as opposed to 16% of men. As for the issue of income levelsand this is particularly the case of jobs in information, the arts and the performing artswomen also earn less than men: 50% of women earn more than 15 000 € as opposed to 60% of men.

Survey methodology

The decision to pursue studies in these areas does not therefore provide the same professional guarantees for men and women, which only serves to reinforce the hypothesis of a lesser competitive advantage for the latter if they choose to pursue independent careers in intellectual and artistic professions, in spite of their specialist training in the area.

Despite being massively present in art subjects, there are relatively few women who find employment in the area, especially in the case of creator-authors. Is it possible to highlight women's withdrawal from these professional markets at the very outset of their careers?

On the face of it, this particular research issue is not easy to address in so far as becoming an artist does not require any specific training, unlike professions in closed markets. Self-teaching remains positively valued in this particular sector, with artists going so far as to omit deliberately from their CV their artistic education or any additional training based on work experience. However, artistic offer has considerably developed in teaching and has created many vocations. Many students from these particular courses envisage pursuing their studies at a higher, postgraduate level. For students who decide to further their artistic skills and knowledge, it appears that the longer they pursue their studies, the keener they become to establish a coherent The rate of female employment is significantly lower than it is for men, with 62% of women having secured employment 18 months after graduation as opposed to 68% of men. Of those who had secured employment, 49% of male graduates worked as independent artists as opposed to just 32% of female graduates. When they opted to work as independent artists, women were less likely than men to work as plastic artists: 31% of women had become plastic artists as opposed to 37% of men. The differences were even more pronounced in the second survey: three years after graduating, the plastic artist/independent artist ratio was 30% for women and 49% for men.

Women appear to be less visible and less integrated in networks promoting reputation and recognition. There are two kinds of independent artists: plastic artists and commissioned artists (designers, graphic designers, essentially). The survey indicates that 36 months after graduation male plastic artists had performed on average 10 exhibitions since graduating, as opposed to just 4 exhibitions for their female counterparts. Male plastic artists also exhibit their work more frequently than women in art galleries, salons and museums, high places of artistic recognition, be they plastic artists (53% as opposed to 36% of women) or designers/graphic designers (33% as opposed to 0%). Male graduates had also taken part more frequently in competitions:

this was the case for 79% of male plastic artists compared to 58% of female plastic artists, and 53% of male designers/graphic designers as opposed to just 33% of female designers/graphic designers. Finally, women claimed they were slightly less integrated in professional networks: 75% of female plastic artists as opposed to 79% of male plastic artists, while just 33% of women produced commissioned work, as opposed to 60% of men.

A second indicator revealing the unequal correspondence between training and employment in art school graduates is designed to establish how men and women tend to promote their skills in salaried employment. In this market, women enjoy a greater sense of stability and less precarity. However, this is achieved at the cost of a degree of resignation since women also stated that they were less frequently required to use their artistic skills than their male counterparts. 36 months after graduation, a significantly higher proportion of male graduates had secured jobs that enabled them to promote their artistic skills (82% of men as opposed to 57% of women).

The same observation also applies in the private realm, where female workers are fewer in numbers than their male counterparts. 18 months after graduation, fewer women stated that part of their leisure time was devoted to pursuing their artistic activities as amateurs (on average 64 hours per month as opposed to 88 hours for men). These differences were shown to be greater still in the second survey since women stated that they devoted very little time to such pursuits (49 hours) in comparison with their male counterparts (97 hours). Female respondents were also less likely (22%) to have a work space or studio at their disposal than male respondents (39%). Beyond the issue of artistic practice, there are also significant differences in the capacity of male and female artists to promote their work. Thus, women stated that they felt less integrated than men in a relational network that was liable to help promote their work (respectively 41% and 55%). Whereas the situation of women in this respect had barely changed 18 months later, the situation of their male counterparts had considerably improved, with 61% of male respondents claiming they felt well integrated within relational networks as opposed to just 42% of women. Women were also less likely to receive remuneration from sales of their work (16% as opposed to 20% respectively), and where earnings were obtained, these tended to be lower on average for women (188 € for women as opposed to 313 € for men). Women exhibited their work four times throughout the 36-month period after graduation whereas men exhibited their work roughly 6 times throughout the same period.

Discussion

An ideology may be defined as a specific set of beliefs held at a given moment within a group or society that is liable to shape individual or collective behaviour. The advent of the artistic professions in the professional domain served effectively to exclude women from the realm of artistic creation and to provide a system of representation and explanation of artistic genius that has remained critically unchallenged by society at large. This is illustrated by the fact that the greatest chefs, painters, choreographers, composers and stylists are still embodied by predominantly male figures in collective representations. The strength of an ideology is to provide subjects with an account of their situation that spares them from having to question the prevailing order of things (Suaud, 1978). The tendency of female artists to avoid the most prestigious careers in spite of a high level of specialisation in these areas is a good indication of the extent to which this ideology continues to exert its hold over the realm of artistic creation.

Following the 'first ideological conversion', artist in popular belief is crossed of the status of manual worker to that of intellectual and slave's rank in that of genius. In this conversion, cultural evolutions of the society moved away the woman from the artistic creation which had the effect of linking genius to masculine faces. These social representations on the creative potentialities of the women continue influencing judgements on their productions and restrict their progression of this fact always in networks.

The ideology of vocations is still highly relevant in the age of equal opportunities, particularly because it is increasingly relegated by socialising institutions. Entrusted with the task of identifying, training and channelling the 'new vocations', these institutions are increasingly attracting an ever growing number of candidates to the profession who wish to complete formal training courses as part of their artistic education (Salamero, 2008). The power of these institutions to confer status and recognition thus helps the myth to endure all the more efficiently since they have undergone a second 'ideological conversion' by replacing the pseudo-religious obscurantism of specialist training courses with certifications and rhetorical practices that promote a meritocratic ideal. However, these degree-awarding institutions have in no way resolved the issue of the dual conception of society that opposes male and female activities.

This explains why, in spite of the high rates of feminisation in art-based courses, there are still fewer women than men in the most prestigious artistic careers. The surveys used for this study (INSEE and art schools) show that these courses entail a high degree of risk for women in so far as they are more likely to be seeking employment after graduation than their male counterparts. In cases where they have secured a job, women are more likely to be positioned in salaried employment, which also means that they are more likely to refrain from promoting their artistic skills in their professional occupation. In the case of independent professions, women appear to be less integrated socially in networks that favour the promotion of their work, thus limiting the likelihood that they are able to gain recognition on the art scene. Finally, in the realm of non-professional activities, women also appear to be less likely to gain recognition on the art market.

Therefore, the crucial factor in the differentiation of men and women still remains the recognition of their skills and their capacity to integrate networks promoting reputation and visibility on the social capital market, more than their opportunities for accessing the profession itself. These cultural obstacles and this lack of control over social relations partly explain why women choose not to pursue the most prestigious artistic careersa retreat that is all the more remarkable that having long been excluded from the institutions of artistic education, women are now over-represented in these institutions.

Thus, far from disappearing as a result of the various feminist and democratic movements in western societies, these elite professions continue to operate a segmentation of the market in such a way that women occupy an unequally advantageous position in comparison with their male counterparts. Female artists are thus confronted not merely with a form of vertical segregation since they are less likely to access the highest levels of valuation than men, but they are also faced with a form of horizontal segregation insofar as they tend to opt out of professional activities where they must face more difficulties to assert themselves. In other words, while there is a 'glass ceiling' preventing them from establishing themselves as recognised artists, women also tend to come up against a 'glass wall'.

While it may call for a reflection on a wider theoretical context including in particular the so-called vocational professions, the analysis of artistic professions primarily provides an opportunity for studying the processes of withdrawal of a group whose acquired rights are threatened by the active demands of an emerging group. Besides its demystification of 'guilty knowledge' [START_REF] Hughes | Professional and Career problems of sociology[END_REF], the rising level of knowledge in modern societies increasingly threatens the legitimacy of occupational groups defined as professions which, in view of the specific nature of their activities, are also likely to be practised by non-professionals. In a vulgarised labour market already open to all forms of competition, the presence of women as a group that is both socially coherent and extensive is only likely to reinforce the protectionist tendencies of those who had previously struggled to establish their hold over the same

Survey 2 :

 2 Of the 169 886 individuals included in the INSEE job survey, 5610 chose to specialise in art, communication or information studies as part of their training towards their final qualification.

  relation between their educational training and their targeted job. The present study will consider one of the highest levels that can be attained in artistic training. The selection process for entering a French Art Schools (Ecole d'Art) is based on admission by a panel of graduates of the secondary education which, three years later, grants students the right to pursue their studies at a higher level (two further years of study). The length of the course and the rigour of the selection process are designed to ensure a high standard of education and training. Survey methodology Survey 3: A specific analysis of individuals with qualifications from art schools consisted of monitoring a cohort of 773 students graduating in June 2005 (the near totality of new graduates). Students were interviewed 18 to 36 months after graduation.

Table 1 : Inequality of positions in professional labour markets

 1

	Specificities of the market	Profession		N	Level of study No secondary education Higher education	% children of managers	Annual income before taxation [0 €-10000 €[ [35000 € and +[
		Agriculture livestock farming	and	1172	34	9	1	45 %	5 %
	Open market	Arts and crafts Business Artistic professions	900 758 229	28 38 18	8 14 51	6 7 31	29 % 41 % 41 %	8 % 7 % 12 %
		Other professions		357	32	26	12	35 %	10 %
		Average		3414	32	15		39 %	7 %
		Health care		532	2	94	24	8 %	44 %
	Closed	Law		51	0	100	28	4 %	54 %
	market	Consultancy		172	8	73	25	23 %	24 %
		Average		755	3	89		11 %	40 %

Table 2 : Rate of feminization in art subjects Rate of feminization Higher education

 2

		Art options in secondary schools	79%
		Institutes of plastic arts and applied arts (=57)	63%
	University training	Music and dance schools (=25) Architecture schools (=20) Theatre and performing arts schools (=12)	55% 51% 49%
		Film and broadcasting studies (=1)	43%
			59%
	Private	Conservatoires in music, dance and drama	Precisely 56% in music, 92% in
			dance and 65% in drama
	education

National institutes of music (which also offer training in dance and drama) 59%

 Suaud, C. (1978), La vocation. Conversion et reconversion des prêtres ruraux. Paris, Les éditions de Minuit. Weber, M. (éd. orig. 1922Weber, M. (éd. orig. , trad. fr. 1971Weber, M. (éd. orig. , rééd. 1995)), Économie et société, Plon, Paris.