Yves Allory

Stéphane Culine

Alexandre De La

St Phane Culine

Alexandre De

La Taille

Kidney cancer pathology in the new context of targeted therapy

Keywords: Renal cell carcinoma, targeted therapy, VHL, HIF, VEGF, mTOR

ouverte pluridisciplinaire HAL, est destinée au dépôt

Kidney cancer pathology in the new context of targeted

therapy.

Introduction

Renal cell carcinoma (RCC) accounts for 2 3 of all malignant diseases in adults ( ). The incidence of all stages of this cancer has -% 1 increased over the last 20 years, contributing to an increasing mortality rate. Twenty to 30 present with metastasis and 20 to 30 relapse % % after curative nephrectomy. The overall 5 year survival ranges from 85 for patients with organ-confined disease, treated by partial or % radical nephrectomy, to only 10 in patients with metastatic disease or relapse after nephrectomy ( ). The renal cancer is not one entity % 2 but rather a collection of different types of tumors (the clear cell, papillary and chromophobe cell types being the most frequent), each derived from various parts of the nephron, with morphological and genetic features ( , WHO 2004 classification and emerging table 1 entities likely to be included in future WHO classification) ( ). Molecular pathology in kidney cancer has developed extensively in the 3 few last years, providing insights in underlying oncogenesis, with new basis for accurate classifications and more effective systemic therapy. However, in renal cancer, the use of targeted therapies in metastasis disease still lacks consistent predictive biomarkers ( ). [START_REF] Atkins | Treatment selection for patients with metastatic renal cell carcinoma[END_REF] review aims to focus on molecular profiles in renal cancer accounting for the effects of targeted therapies and substantiating the search for relevant predictive biomarkers.

Classification and clinical trials

Advanced disease is refractory to radiotherapy and known chemotherapies, and the only treatment available for metastatic disease has been for a long time immunotherapy based on interleukin-2 (IL-2) and/or interferon-(IFN-), with durable response for less than 10 of α α % patients. In years 2000s, a new paradigm has emerged in renal cancer with the use of effective targeted therapies, including anti-angiogenic agents (the anti-VEGF A antibody bevacizumab and VEGFR2 tyrosine kinase inhibitors sunitinib and sorafenib) and mammalian Targets Of Rapamycine (mTOR) inhibitors (temsirolimus and everolimus). Most of these drugs are used currently as first line treatment in metastatic disease ( , see current recommendations). A comparison of over-expressed genes in the three most frequent subtypes of table 2 renal cell carcinoma showed both common and specific sets of genes between clear cell, papillary and chromophobe cell carcinomas, suggesting the potential importance of tumor subtyping when investigating biomarkers and targeted therapies ( ). Thus, the beneficial 5 effects of VEGFR inhibitors sunitinib and sorafenib have been demonstrated for patients with clear cell RCC in distinct settings ( ), table 2 and appeared more limited for patients with papillary or chomophobe cell RCC ( ). On the opposite, temsirolimus regimen seems to 6 demonstrate a more significant effect on median survival for patients with non-clear cell RCC (including 75 papillary RCC), than for % patients with clear cell RCC ( ). Clinical trials are currently recruiting patients to assess precise effect of mTOR inhibitors on metastatic 7 papillary RCC.

Meanwhile, the pathological classification of renal cancer has been extended significantly with the description of new entities based on histological and/or molecular criteria ( ) ( ). The diagnostic features of the new entities have been reviewed recently ( ). Of note, table 1 3 8 some cases previously considered as clear cell carcinoma or papillary carcinoma should be diagnosed according to up-dated criteria, as carcinoma associated with translocation or , papillary carcinoma with clear cell, or carcinoma associated with acquired TEF3 TFEB multicystic disease, for instance. A fraction of cases included in the clinical trials would be re-classified now in new entities, with a potential impact on the trial conclusions according to histological subtypes. Retrospective analysis of former trials on the basis of pathological re-examination and new prospective trials should be performed to precise the relevance of the available therapies according to the different subtypes and prognosis groups of tumors. Overall, the context of intense research for consistent biomarkers predictive for a treatment response underscores the interest to provide accurate pathological diagnosis based on morphological, immunohistochemical and genetic features ( ). 10

Genetic changes in sporadic and hereditary renal cancers

The genetic studies in sporadic and hereditary forms of renal cancer have settled a relevant framework to integrate renal cancer pathology in the era of targeted therapy, providing a rationale for the treatments and suggesting potential predictive biomarkers. The recurrent cytogenetic changes in sporadic forms support the distinction of the different subtypes of renal tumor identified historically on morphological examinations ( ). A few key genes have been identified, in particular with the investigation of hereditary kidney table 1 cancer syndromes who rare clinical entities (2 3 of all renal cancer cases), but offer valuable insights into the pathogenesis of kidney shows frequent inactive VHL, and active hypoxia and VEGF pathways ( ). Interestingly, a recent genome-wide analysis of copy-number 13 changes and gene expression profiles has shed light on the clear cell RCC subtype, showing that sporadic clear cell RCC without evidence of bi-allelic VHL inactivation fell into two groups, one group with genomic profiles that are much more similar to tumors with bi-allelic inactivation of VHL, and the other group with genomic profiles highly dissimilar to the majority of clear cell RCC ( ). 14

The oncogene (7q31) is frequently gained and occasionally mutated [START_REF] Furge | Identification of deregulated oncogenic pathways in renal cell carcinoma: an integrated oncogenomic approach based on gene expression profiling[END_REF] in sporadic papillary RCC (type 1). For the tumor c-MET % suppressor gene no mutations in sporadic RCC have been detected but the FH pathway is frequently under-expressed in papillary RCC FH, (types 1 and 2) ( ). Inactivating mutations of the gene have been detected in sporadic chromophobe cell RCC [START_REF] Young | Analysis of VHL Gene Alterations and their Relationship to Clinical Parameters in Sporadic Conventional Renal Cell Carcinoma[END_REF], suggesting a 13 FLCN % tumor suppressor role, at least for the chromophobe subtype oncogenesis ( ). AKT-mTOR and c-myc appear also to be activated 15 pathways both in fractions of clear cell and high grade papillary RCC ( ). These signaling pathway alterations, whether specific or not 13

for the different tumor subtypes, provide prime targets for systemic therapy in advanced disease.

VHL and HIF pathways

The loss of VHL (resulting from inactivation of both alleles) is a critical event in the pathogenesis in most clear cell RCC ( ). The 12 consequences include effects on the Hypoxia Inducible Factor (HIF) and HIF independent effects. HIF is a heterodimeric transcriptional factor associating HIF1 (or HIF2 ) with the partner HIF1 . The VHL gene product is a component of an E3 ubiquitin ligase complex that α α β targets HIF1/2 subunits for polyubiquitylation and proteasomal degradation ( ). This process is dependent on the hydroxylation of α 16 conserved proline residues on the subunits of HIF1/2 in the presence of oxygen. When oxygen levels are low, or VHL is inactivated,

α α
HIF1 or HIF2 accumulate, form a heterodimere with HIF1 and translocate into the nucleus to regulate specific targets through binding

α α β
to the hypoxia-responsive elements (HREs) located in the promoter/enhancer regions of hypoxia-inducible genes ( ). HIF1 or HIF2 17 α α share significant homology and regulate partially overlapping repertoires of hypoxia-inducible target genes but may have distinct effects on RCC cell growth ( )( ). HIF3 is a third HIF who probably acts as a dominant negative inhibiting the effects of HIF1 and HIF2 . another small kinase inhibitor, displays an activity against VEGFR2, VEGFR3, PDGFR-B, FLT-3, c-KIT and RAF-1, assumed to account for the prolongation of progression free survival observed both in previously untreated and cytokine refractory metastatic clear cell RCC patients ( )( ). [START_REF] Escudier | Sorafenib for treatment of renal cell carcinoma: Final efficacy and safety results of the phase III treatment approaches in renal cancer global evaluation trial[END_REF] 1

The interest of available anti-angiogenic therapy in the adjuvant setting for tumors at risk of progression after curative nephrectomy is under investigation. Moreover, almost all kidney cancer patients treated by VEGF inhibitors experiment disease progression, and further strategies should include attempts to identify new gene/pathway addiction created in cells defective for VHL protein function, and to inhibit compensatory mechanism that promote tumor survival in the setting of VEGF pathway blockade. Interestingly, the HIF-independent effects of VHL loss remains poorly understood, but could involve the activation of NF B pathway promoting survival, in κ particular with the removed inhibition of the NF B agonist Card9 ( ). A recent study pointed also at VHL loss consequences in mitotic Regarding the gene status (inactivated by mutation or methylation wild type), complex results has been reported. Choueiri et VHL versus al. have found no association between VHL status and response rates or median progression free survival, but the presence of loss of " function mutations was an independent factor associated with improved response ( ). Also, the VHL gene status could be relevant for " 26 patients treated by sorafenib and bevacizumab, and not for patients treated by sunitinib, and new tested inhibitors axitinib or pazopanib ( 4)( ). These differences could underlie non-VHL related antitumor effects for sunitinib, axitinib and pazopanib, or be explained by a 27 variable drug sensitivity of VHL/HIF/VEGF pathway in VHL wild type RCC. Overall, these data support the need for further studies investigating the relationships between VHL gene status and anti-angiogenic therapeutic response.

As already mentioned, the clinical effects of anti-angiogenic drugs for patients with papillary RCC seem to be limited ( ). Of note, the 6 fumarate hydratase activity (which is decreased significantly in papillary RCC) is related in part to HIF pathway: FH inhibition leads to elevated intracellular fumarate, which in turn acts as a competitive inhibitor of HPH (HIF prolyl hydroxylase), thereby causing stabilization of HIF (Hypoxia-inducible factor) by preventing proteasomal degradation ( )( )( ). Elevated HIF drives transcription of 28 29 30 key components of the glycolytic pathway, including GLUT1 and lactate dehydrogenase (LDH), inducing a Warburg effect (the tendency of cancer cells to rely on glycolysis as their energy source). However, there are probably other tumor suppressor roles of FH, probably HIF independent, and involving in particular the DNA damage response ( ). 31

mTOR pathway

The PI3K-AKT-mTOR cascade appears to be another pivotal pathway in clear cell, but also non clear cell RCC. Upon the binding of ligands on membrane growth factor and/or cytokine receptors, the phospho-inositide 3 kinase generates PIP3 and activates AKT. PTEN is a phosphatase that promotes the generation of PIP2 from PIP3, regulating negatively the cascade. The phosphorylated AKT activates the mTOR complex 1 (mTORC1) through inhibition of TSC1/TSC2, and mTORC1 activates protein synthesis through phosphorylation of key regulators such as the P70 S6 kinase (S6) ( ). Activated phosphorylated S6 (phospho-S6) exerts a negative feed-back loop on IRS1/IRS2 32 receptors upstream to PI3K. Of note, the targets of S6 include the factor HIF1 , explaining why HIF1 expression is dependent on the α α mammalian target of rapamycin (mTOR) and sensitive to rapamycin or rapalogues such as temsirolimus or everolimus. This effect could account at least partially for the activity of mTOR inhibitors in kidney cancer. Phase III trials has shown that temsirolimus improves overall survival in patients with advanced RCC and poor prognostic features, and everolimus improves progression-free survival in patients for which sorafenib and/or sunitinib become ineffective, both in clear cell and non clear cell RCC ( )( )( )( ). Furthermore, 7 33 34 35 as the signaling downstream to VEGFR involves the PI3K-AKT-mTOR pathway, the mTOR inhibitors might theoretically affect both tumor cells and tumor associated endothelial cells. Pantuck et al. have studied the activated status of mTOR pathway, using phospho-S6 as a marker this activation. Phospho-S6 was associated with tumor stage, grade, and disease specific survival in patients with localized or metastatic disease ( ). A small retrospective analysis has suggested that high expression of phospho-AKT or phospho-S6 could be 36 associated with response to temsirolimus ( ). The value of these biomarkers and other candidates within the PI3K-AKT-mTOR pathway 37 must be validated in larger retrospective and prospective studies. The PTEN expression does not seem to have any predictive value in that context ( ). 38

Besides mTORC1, mTORC2 is another mTOR complex in the pathway, with ability to activate AKT through phosphorylation. There are some evidences that HIF1 expression is dependent on both mTORC1 and mTORC2, and HIF2 expression is dependent only on α α α explanation for a resistance to mTORC1 inhibitors. Furthermore, the action of mTORC1 inhibitors on S6 results in loss of feed-back inhibition and AKT phosphorylation through the mTORC2 ( ). These considerations underscore the importance of targeting mTORC2 32 (inhibitors targeting both mTORC1 and mTORC2 are under investigation), and probably to combine treatment with new inhibitors of IRS1/IRS2 or PI3K.

The mTOR inhibitors could be of interest to treat metastatic chromophobe cell carcinoma, but the data are still limited ( ). Of interest, 7

mouse models deficient for the gene have been developed, developing oncocytic cysts and renal tumors, and mimicking the FLCN Birt-Hogg-Dub (BHD) syndrome which predisposes subjects to develop renal carcinoma of nearly all subtypes (the chromophobe cell é RCC subtype being the most frequent in BHD nevertheless) ( )( )( )( ). The tumor suppressor role for FLCN was demonstrated, 40 41 42 43 but contradictory results regarding the role of FLCN in PI3K-AKT-mTOR pathway have been described, with the mTOR target phospho-S6 being increased or decreased upon the context and/or the model. Additional studies are mandatory before considering that inhibitors of both mTORC1 and mTORC2 might be effective as potential therapeutic agents for BHD-associated kidney cancer.

Myc pathway

A c-MYC gain (8q24) has been significantly observed in up to 20 of clear cell RCC either by genome wide or specific FISH % analysis, and correlated with concomitant over-expression, suggesting its involvement in renal oncogenesis ( )( ). Moreover, pathways 14 44 analysis and experiments in cell lines support the activation of c-MYC pathway, resulting in cell cycle promotion ( ). Recently, a study 13 has demonstrated elegantly that HIF effects on c-myc could distinguish two subtypes of sporadic VHL-deficient clear cell renal α carcinoma : the fraction of VHL-deficient clear cell RCC with co-expressed HIF1 and HIF2 could activate the AKT/mTOR and α α ERK/MAPK pathways and be likely to respond to anti-angiogenic and mTOR inhibitors, the fraction of VHL-deficient clear cell RCC with HIF2 expressed alone could promote the myc transcriptional activity, with higher rates of cell proliferation and tumor growth ( ).

α 45
The authors suggest that this molecular stratification according to HIF1 /HIF2 expression could provide a framework for sub-classifying

α α
tumors for targeted therapy. The pertinence of these two subtypes of clear cell RCC in regards of therapeutic response to mTOR inhibitors or anti-angiogenic remains to be tested. Furthermore, high grade papillary renal cell carcinoma (type 2) has been shown to be associated also with c-MYC signature ( ). This signature was correlated with gain of chromosome 8q and overexpression of c-MYC located in 46 8q24. Overall, these observations raise the potential interest of future therapy targeting the c-MYC pathway in a fraction of clear cell and high grade papillary RCC, using MYC inhibitor or siRNA strategy, for instance.

c-MET pathway

Activating mutations in the tyrosine kinase domain of the gene (7q31) have been detected in the germ line of affected c-MET individuals in hereditary papillary renal cell carcinoma kindred and in tumors from patients with sporadic type 1 papillary renal cell carcinoma. c-MET is the receptor for the hepatocyte growth factor HGF (7q21.1), and the HGF/c-MET signaling pathway is involved in proliferation, survival, cell growth, differentiation and cell migration. The involvement of HGF/c-MET pathway in papillary RCC oncogenesis is supported by the frequent trisomy of chromosome 7 observed in sporadic type 1 papillary RCC, but the modest rate of mutation ( 13) could suggest that other major pathways are to be investigated in the sporadic papillary RCC. Most of the inherited c-MET % cases are low grade tumors occurring rather in the 5 decade. However, an early-onset HPRC phenotype has been described, including

Immune response

Immunotherapy aims to elicit an anti-tumor immune response resulting in significant disease remission. The most consistent antitumor activity has been reported with interferon (IFN-) and interleukin-2 (IL-2). The superiority of sunibitib, temsirolimus, and bevacizumab have demonstrated a durable response in 7 8 patients, supporting the use of this cytokine therapy for some patients with metastatic RCC -% ( )( ). Of note, IL-2 is the only therapy for kidney cancer that can produce a remission of disease that lasts after treatment is 53 54 completed. According to published data, immunotherapy should be restricted to patients with metastatic RCC, good risk and clear cell subtype. Moreover, in clear cell RCC, the additional predictive features of better response to high-dose IL-2 could be an alveolar pattern > 50 , no granular of papillary features, and an expression of carbonic anhydrase IX (CAIX) in immunohistochemistry in > 85 of tumor % % cells ( ). Indeed, in one study, the response rate was 59 for patients with good-risk and high-CAIX expression versus less than 5 for 55 % % patients in the poor-risk group with low CAIX expression ( ). A current high-dose IL-2 trial is investigating currently its efficacy 55

according to these predictive features to validate prospectively the selection criteria, and to identify the patients susceptible to benefit the most of immunotherapy. A recent study based on proteomic approach attempted to identify new biomarker in the immunotherapy setting (

). 56

Conclusion

During the ten last years, the intense research in renal cancer area has provided a huge amount of new molecular knowledge, providing rationale for targeted therapy in metastatic disease. Though no tissue biomarker can be recommended currently to predict therapeutic response, CAIX expression for high dose IL-2 immunotherapy, gene status and HIF2 expression for anti-angiogenic drugs, and VHL α phosphorylated protein S6 expression for mTOR inhibitor use, are the leading candidates under investigation. Besides tissue analysis in progress, other useful biomarker studies include clinical features, functional imaging and blood investigations. Parallel to the emergence of targeted therapy, the classification of renal turmors has been precised both on morphological and molecular basis, appearing more complex than 10 years ago, and the design of future clinical trials should take into account this variety of tumor subtypes to provide the most relevant conclusions. Meanwhile, the pathways involved in renal cancer are amazingly intermingled and shared at least partly by the different tumors subtypes, suggesting common oncogenetic determinants and the possibility to use the same drugs for different diseases.

Future studies will investigate combination and sequential therapy, mechanisms of resistance, and their effects in adjuvant or neo-adjuvant settings.

κ 24 spindle 4 α 4 α

 2444 disorientation and promotion of genetic instability ( ).[START_REF] Thoma | VHL loss causes spindle misorientation and chromosome instability[END_REF] Another current issue is the validation of tumor biomarkers predictive of response to anti-angiogenic therapy. Recent studies have proposed clinical (time from diagnosis to VEGF-targeted therapy < 2 years, two or more metastatic sites, ECOG PS>0) and biological (neutrophils > 4.5 K/ L, platelets count > 300 K/ L, abnormal corrected plasmatic calcium level, LDH > 1.5 upper limit of normal) μ μ criteria that should be tuned by tumor molecular features ( ). The molecules HIF1 , VEGF, VEGFR2, CAIX, all involved in the signaling cascade expression, have been tested in pre-therapeutic tumor samples, but their expression fails to predict a therapeutic response for patients submitted to anti-angiogenic treatment ( ). Only the high HIF2 expression (assessed by western blot) has been reported to be associated with sunitinib response in a small cohort of 43 patients, and the plasmatic levels of soluble forms of VEGFR2 and/ VEGFR3 at initiation or during the first weeks of systemic treatment have been proposed also to be predictive of therapeutic response ( ). These 4 results should be confirmed by further studies, and the current clinical trials aim to identify and/or validate such predictive biomarkers.

49 "

 49 th metastasis progression ( ). Likewise, most sporadic type 1 papillary renal cell carcinomas are associated with favorable outcome, but a 47 recent study reports on metastatic type 1 papillary RCC with outcome even worse than for metastatic type 2 RCC ( ). Even unusual, 48 such metastatic type 1 papillary RCC are good candidate to be treated by drugs targeting the c-MET pathway, according to different strategies, antagonism of ligand/receptor interaction, inhibition of tyrosine kinase catalytic activity, and blockade of receptor/effector interactions ( ). Such options are under current investigations in clinical trials. The c-MET receptor could belong to the dependence receptor family, and the blockade of the pathway is expected to promote apoptosis in tumor cells ( ). Furthermore, a recent screen " 50 detected c-MET as a kinase required for survival in VHL defective renal cancer cells, suggesting the interest to target c-MET pathway also in clear cell RCC ( ). A cooperation between FH and c-MET in transformation and tumorigenesis was demonstrated also in a cell line 51 model, underscoring how the pathways can interplay and the potential interest of combined targeted therapy ( ). 52

  α α plus IFN-over IFN-alone has limited the role of single-agent IFN-. However, trials with high-dose intravenous bolus interleukin-2 α α α

8 mTORC2 ( ). As temsirolimus and everolimus are only active on mTORC1, HIF2 is not targeted by these therapies, providing

fumarate in regulation of HIF stability . Cancer Cell . 2005 ; 8 : 143 -153


Raphaël Hoarau
email: raphael.hoarau@enac.fr

Stéphane Conversy
email: stephane.conversy@enac.fr

Augmenting the scope of interactions with implicit and explicit graphical structures

Keywords: ACM Classification: H5.2 [Information interfaces and presentation]: User Interfaces. -Graphical user interfaces. H.5.2. User Interfaces: Interaction Styles. General terms: Design, Human Factors Graphical Interaction Design, Instrumental interaction, Exploratory Design

When using interactive graphical tools, users often have to manage a structure, i.e. the arrangement of and relations between the parts or elements of the content. However, the interaction with structures may be complex, and not well integrated with the interaction with the content. Based on contextual inquiries and past works, we have identified a number of concepts and requirements about the interaction with structure. We have explored two interactive tools: a new kind of property sheet that relies on the implicit structure of graphics; and a property delegation graph to enable users to provide an explicit graphical structure. The interactions with the tools augment the scope of interactions to multiple objects.

INTRODUCTION

When using computerized tools such as real-time editors, presentation software, GUI builders, etc. users create and manipulate graphical objects on the screen. They can edit them individually, e.g. change their color or their stroke width. Users can also consider and interact with sets of objects as opposed to individual objects. To do so, they may be required to structure the scene, by relying on concepts such as groups, styles, or masters. According to the Oxford dictionary, a structure is "the arrangement of and relations between the parts or elements of something complex". Using a structure may have multiple assets, such as helping users conceptualize the scene they are creating ("the background of the slide includes this drawing and this text", "this set of slides is a subpart of the presentation" etc.), and think better about the problem at hand. Here, we are interested in structures as means to interact with the content: since structuring involves sets of objects, the actions done on an element of the structure may have an effect on several objects at once.

In current interactive systems, the use and the management of structures may be complex. Users have to create and maintain them. Depending on the kind of structure, some operations may be impossible or cumbersome to do, which prevents users to explore the design space. Furthermore, systems that provide structuring do not leverage off the structures fully to provide users with new ways of interacting with the content.

Interactions with structure and multiple objects through a structure have not been studied extensively in the past. Of course, there exists works that implicitly tackle the problem, but few concepts or properties explicitly target it. For example, what are the interactions that enable users to define sets of objects? What are the available means to augment the scope of interaction i.e. apply an interaction to several targets? What are the concepts that may guide the design of interactions?

The work presented in this paper aims at improving the management of structures as means to augment the scope of interactions. Based on contextual inquires and related work, we present a number of requirements pertaining to the interactions with structures. We then present a set of interactive tools that partly fulfill those requirements. In particular, we present two new visualizations of properties and values. Together with modeless, example-based interaction and selection, they enable designers to make an opportunistic use of implicit (i.e. unplanned) sets of objects, and to structure the content explicitly.

WORK SCENARIOS

We have based our work on concrete and realistic case studies. We have conducted five contextual inquiries with "designers", the design activity being taken in its broadest sense: graphics edition (Illustrator and OmniGraffle), courses schedule (iCal), geographical map of a site (Auto-CAD), lecture presentation (PowerPoint). In order to introduce the problem and concretize it, we present two of the five case studies with work scenarios, which illustrate interactions on several objects with or without a structure. Some of the steps are annotated with words in italic to characterize them. We detail the annotations later in this section.

Software keyboard

The first scenario describes the creation of the graphical part of a software keyboard, such as the ones available on tablets. The user is a designer that employs a graphics editor (here Illustrator). The user begins by creating a fist key. She draws a round rectangle, applies a gradient to the rectangle, and adds a surrounding rectangle (stroke only). She selects the two rectangles with a selection rectangle (designation), and groups them with a group command in a menu (structuring). She then adds a soft shadow effect on the group. She overlays a label with a text 'A' on the group of rectangles, and centers the label and the group by invoking a center command on a toolbox. She then forms another group with the label and the groups of two rectangles, and names it "key", in the tree view of the graphical scene provided by Illustrator (structuring). This first key serves as a model to create other keys: the user duplicates the key, and applies a horizontal translation to the copy. She proceeds with this action several times in order to form a row of keys (Figure 1). She then modifies the text of each key one by one, until she gets an 'AZERTYU' keyboard. However, when she changes the letter 'A' for the letter 'I', she realizes that the 'I' text is not centered with the rectangles (Figure 2). The first object was specified incorrectly: if the three objects (label, background rectangle, stroked rectangle) are correctly aligned, the text of the label is not centered. With the first letters (AZERTYU), the problem was not existent since the widths of the texts are similar. The user could realize the problem only when tackling a thinner letter ('I').

Each label being into a heterogeneous group (containing other object types than label), the system does not provide a text center command that can be applied to a selection of objects. She has to click multiple times on an object to reach the label and apply the 'text centered' command. Therefore, she estimates that it is more efficient to start over: she deletes all copies, un-groups the first key, centers the text, groups the objects again, copies et moves the copies, and modifies each letter one by one. This scenario illustrates several tasks that the user should accomplish.

Sets management

The user relied on the ability of the system to allow sets creation, modification, and management. For example she created a single group with two rectangles, then another group with the previous one and the label. She could also name them, both because it is a way to conceptualize information, and to be able to reference it in a toolkit that displays SVG graphics. Operations on groups include destruction (on the canvas view), and reparenting of the hierarchy (on the tree view).

Designation The user designated properties, actions, and objects. For example, she changed the "alignment" property of the label to "centered".

Scope of actions Some actions allow the user to act on multiple objects at once. For example, the user grouped objects because she wanted to consider them as a single entity that keeps relative position between subparts, but also because she wanted to apply a single translation on three objects at once. Conversely, she was not able to apply the command 'set alignment' to several objects at once.

ATC strips drawing

In this scenario, the user is a visualization designer that aims at designing several enhancements of paper-strips design for Air Traffic Control. A paper strip is a tool that helps controllers verify that flights are not in conflict, i.e. their planed time of passage over beacons are not the same. He wants to design and illustrate a new digital representation with colored gradients that would show the current position of the flight between two beacons. Figure 4 shows the final result. The user starts with the drawing of a simplified strip, by imitating an actual one (see Figure 3). The strip is composed of lines, rectangles, and labels with textual informa-tion. He duplicates the first strip multiple times, and stacks the copies in order to form a strip board (Figure 4, left). He then modifies the labels to reflect information about other flights. While thinking about his design, he elaborates a new one, based on the first version: right aligned beacons (Figure 4, right), instead of left aligned beacons (exploratory design). Compared to the first version, the new design would enable controllers to rank easily the flights by their order of airspace exit (the righter the sooner). Thus, he duplicates the previous board, and modifies each strip to right align beacons.

While trying to show the value of using gradients, he realizes that the design should involve two flights in conflict. To do so, he has to make the time of passage over certain beacons match. He first proceeds on the second version on the board. However, he wants stakeholders to be able to compare the two designs. In order to limit the differences between the two versions, he has to change the first board accordingly. He begins by searching the elements that must be changed (searching).. When he finds one, he executes the actions required to apply the modification.

Besides the tasks already evoked in the first scenario, the second scenario illustrates two new activities.

Seeking/designation The user needs to retrieve objects, based on explicit or fuzzy requirements. In the scenario, he has to search objects whose content (here a text) is similar to other ones. The search action requires scanning visually the graphical objects in the board and seeking candidate objects, at the risk of forgetting some of them. As the number of objects increase, it is more and more difficult to seek object with visual scanning. In the previous scenario, each modification becomes more costly, not only because of the number of actions to repeat, but also because of the required search effort.

Exploratory Design The user explores parts of possible solutions, and modifies existing parts of solutions. In doing so, he pursues an exploratory design activity. By combining action, visualization of intermediate results, and thinking, exploratory design generates a co-discovery of the problem and the solution. This phenomenon is important for activities in which the expected result is not known in advance: graphics edition activities, but also during slides design, or class hierarchy design [START_REF] Green | Cognitive dimensions of notations, in People and computers v[END_REF] [START_REF] Terry | Recognizing creative needs in user interface design[END_REF].

RELATED WORK

Past works have tackled the problems of managing structures, and interacting with multiple objects, either explicitly or implicitly. We have studied the existing systems along three axes: interactions for structuring the content provided by interactive systems, design and evaluation of interactions for structuring, and structuring in programming, since many concepts from this domain are relevant.

Structuring for users

Groups In order to act on several objects at once, traditional graphical editors allows acting on a selection of objects previously defined by the user, or on groups. The only op-erations available for a group is 'ungroup', which removes the group entity and selects all objects that were part of the groups (no modification, addition, or subtraction). Selection can be seen as a temporary group, with 'add' and 'remove' operations e.g. by holding the shift key and selecting several elements, or holding the ctrl key and clicking on individual elements. Translation, scale and rotation can be applied on a group: all elements inside the group are transformed accordingly. Conversely, some operations like 'set color' cannot be applied to groups, supposedly because some elements inside the group do not "understand" this operation. This forces the user to un-group groups, and to apply the command on each objects. In this case, the interaction with the structure is not well integrated with the interaction with the content.

Hierarchy and groups of groups Groups can be part of a surrounding group, turning them into hierarchies. Support for management of such hierarchies range from no support at all, navigation in the parents hierarchy (clicking several times on an object enables cycling through parents in the Squeak version of Morphic [START_REF] Maloney | Directness and liveness in the morphic user interface construction environment[END_REF]), to tree views in structured graphics editors such as Inkscape or Illustrator. A tree view enables user to re-parent elements with a drag and drop. However, there is no support for other operations, such as applying a color to a node in order to change all children.

Masters and DAG A Master is an element used as a "model" for other elements. For example, PowerPoint enables users to define the appearance in a master slide that other slides would inherit. Sketchpad introduced masters as shareable objects that could be used in multiple locations in the scene [START_REF] Sutherland | Sketchpad: a man-machine graphical communication system[END_REF]. Changing a property of the master would modify all objects that depend on this master. This was a way to reduce the number of actions required from the user when something must be changed. Somewhat related to Masters, constraints can also be defined with a link between cells in a spreadsheet [START_REF] Myers | Graphical techniques in a spreadsheet for specifying user interfaces[END_REF]. Masters can be considered as a way to structure contents with a Directed Acyclic Graph.

Properties Presto is a document management system that enables users to tag documents with properties, e.g. year=2011 [START_REF] Dourish | Presto: an experimental architecture for fluid interactive document spaces[END_REF]. Properties provide a uniform mechanism for managing, coding, searching, retrieving and interacting with documents. For example, users can define directories (i.e. a set) of documents using properties: either by extension (by putting elements into the directory), or by intension (with a query such as size >500k). Conversely to purely hierarchical structures, properties enable objects to be part of several overlapping sets. [START_REF] Kurlander | Graphical Search and Replace[END_REF] allows users to search for elements based on their graphical properties (designation). The resulting selection allows the user to change at once a particular property for all found objects (multiple scopes).

Graphical search Graphical Search & Replace

User-defined macros and Programming by example Userdefined macros allow for automation of repetitive tasks.

Programming by example allows non-experts to automate the creation of macros [START_REF] Lieberman | Your Wish is my command: Programming by example[END_REF]. The user proceeds with an example of the task to repeat, and an algorithm abstracts the actions, so as to enable application on other objects. Programming by example relies on a correct interpretation of user actions by the machine. By contrast, our work aims at providing an instrumentation that does not rely on the intelligence (often not sufficient or incorrect) of the system.

Structuring with exploratory design Some structuring techniques have been design to support exploratory design. The list of reversible actions is an important mechanism [START_REF] Shneiderman | Direct manipulation: a step beyond programming languages[END_REF] [START_REF] Kurlander | A History-Based Macro By Example System[END_REF]. Side Views displays previews of interactive commands [START_REF] Terry | Side views: persistent, ondemand previews for open-ended tasks[END_REF]. Parallel Paths is a model of interactions to support alternative exploration [START_REF] Terry | Variation in element and action: supporting simultaneous development of alternative solutions[END_REF]. It lies on an arborescence of creations, instead of a linear process, and on the simultaneous views of parallel results (comparison). Acting on a node "before" a split of the creation path enables users to manipulate the subsequent designs at once (scope).

Structuring for designers

Interaction designers have already identified the need for many modifications with a low number of actions. For example, the ergonomic criteria "brevity", and more precisely the sub-criteria "minimal actions", describes the needs to limit the number of steps of an interaction [START_REF] Bastien | Critères Ergonomiques pour l'Évaluation d'Interfaces Utilisateurs[END_REF].

Cognitive dimensions In the cognitive dimensions of notation [START_REF] Green | Cognitive dimensions of notations, in People and computers v[END_REF], the problem described in the software keyboard scenario is identified as "viscosity". It exhibits when the structure of the information contains a lot of dependences between parts, which implies that a small change leads to numerous adjustments from the user. Viscosity is a hurdle to modification and exploratory design [START_REF] Green | Cognitive dimensions of information artifacts: a tutorial[END_REF]. Since it may be costly to apply the changes, the user refrains from exploring alternatives.

In order to reduce viscosity, a solution consists in creating an "abstraction", a "power command" that would act on several objects [START_REF] Green | Cognitive dimensions of information artifacts: a tutorial[END_REF]. An abstraction is a class of entities, or a grouping of elements that users will handle as a single unit. This will not only reduce viscosity, but also make the notation closer to the conceptual model. Styles in a word processing application are an example of abstraction.

Abstraction can be costly. First, abstractions must be learnt. For example, a novice user will not be able to use the "style" abstraction if he does know that it exists, or how to use it. Their creation and modification requires time and effort. The investment in abstraction management (thinking, building, modifying) should be balanced with investment in repeating a small sequence of actions to solve a small problem. Besides, abstractions can represent a hurdle to exploratory design, if they are required before any other simple actions. For example, the use of classes in objectoriented languages forces users to think about abstract descriptions, before instancing and experimenting them (also known as premature commitment). Finally, abstraction may introduce hidden dependencies: some parts of the scene may depend on others in an invisible way, which makes it hard for the user to predict the effect of a change.

Instrumental interaction and design principles Direct [START_REF] Shneiderman | Direct manipulation: a step beyond programming languages[END_REF] and instrumental [START_REF] Beaudouin-Lafon | Instrumental Interaction: An Interaction Model for Designing Post-WIMP User Interfaces[END_REF] interactions techniques are efficient at interacting with a single object: they lower the number of actions required from the user compared to other techniques, such as command lines, conversational dialogue, or modal interactions. Design principles related to instrumental interaction, such as reification (turning an object into a thing), polymorphism (applying the same change to different class of objects) and reuse (of past selection and interactions result), cope partly with actions on multiple objects [START_REF] Beaudouin-Lafon | Instrumental Interaction: An Interaction Model for Designing Post-WIMP User Interfaces[END_REF]. Reification of concepts into instruments allows for actions on instruments that in turn will act on other objects. Reifying concepts into first-class manipulable objects extends the possibilities of actions. The degrees of temporal and spatial indirection, compatibility and integration enable users to predict the effectiveness of a given instrument. Reification can be considered like enabling direct manipulation of an abstraction (of Cognitive Dimension). Polymorphism enables designers to augment the scope of actions with heterogeneous groups. The number of actions to perform is reduced with polymorphism, since this avoids repeating for each type of objects a change with similar results. Similarly, reuse reduces the number of actions required to manage objects sets (creation, modification).

Cost of interaction techniques

A particular technique is not absolutely better than another, but may be better with respect to the task to accomplish: copy, modification, or problem solving (equivalent to exploratory design) [START_REF] Mackay | Which interaction technique works when?: floating palettes, marking menus and toolglasses support different task strategies[END_REF]. CIS is a model that helps describe an interaction technique, analyze it, and predict is efficiency in the context of use [START_REF] Appert | Context matters: Evaluating Interaction Techniques with the CIS Model[END_REF]. An interface is defined as a set of manipulable objects of two types: work objects (e.g. graphical shapes), and tool objects (e.g. a menu item). There are two types of action: selection, which identifies a subset of the interaction space (moving an object, such as a cursor onto a tool) and validation, such as a mouse click, that confirms the selection action.

CIS defines four properties for interaction techniques. Order and parallelism characterize the scheduling of actions. Persistence indicates whether the technique modifies attributes of tool objects, which has an effect on subsequent interactions. Fusion is the ability of a technique to modify several work objects by defining multiple manipulations at once (similar to scope). Development corresponds to the ability offered to the user to create copies of tools object with different attribute values.

Structuring for programmers

The problems raised so far can also occur during development activities. For example, refactoring tools in IDEs is an answer to the need for multiple scopes of action: if the user changes say the name of a method of a class, the system will apply this change on each reference of the method, possibly in other classes or files. Styles and models can be implemented in a style language (e.g. CSS), with a hierarchical structuring. Changing a parameter in an intermediate node has an effect on its children. Tags in the Tk toolkit allows the programmer to structure objects in overlapping sets (an object can belong to multiple sets) [START_REF] Ousterhout | Tcl and the Tk Toolkit[END_REF]. Changes can be applied to graphical shapes or to a tag, and thus to the set of objects that hold this tag (scope). Tags can be defined by extension (with designated objects) or by intension (with a predicate e.g. all blue objects) [START_REF] Appert | SwingStates: adding state machines to the swing toolkit[END_REF].

Prototype-based languages offer an alternative to classbased languages for object-oriented programming [START_REF] Lieberman | Using prototypical objects to implement shared behavior in object-oriented systems[END_REF] [START_REF] Myers | Declarative programming in a prototype-instance system: object-oriented programming without writing methods[END_REF]. They offer a flexible creation model that allows sharing of properties and behaviors. Such mechanisms allow users to structure a hierarchy of prototypes and to act on several clones by manipulating a prototype in the delegation hierarchy. Morphic [START_REF] Maloney | Directness and liveness in the morphic user interface construction environment[END_REF], the graphical interface of Self [START_REF] Ungar | SELF: The Power of Simplicity[END_REF], reifies prototypes and clones into graphic objects (called Morphs), and allows for their construction and edition with direct manipulation. Tools have been designed to help structure a prototype hierarchy. For example, Guru is an algorithm that automatically creates a well-organized graph of prototypes, by factorizing shared properties into new prototypes [START_REF] Moore | Automatic inheritance hierarchy restructuring and method refactoring[END_REF].

REQUIREMENTS

In this section, we synthesize the requirements for the manipulation of objects through structures. The synthesis is derived from the contextual inquiries we ran, and our analysis of the related work.

R1: Managing sets of objects

Managing sets consists in searching (R1.1), and designating (R1.2) the objects that are part of a set. It is also necessary to modify (R1.3) the sets (add, remove elements). Finally, users must be able to identify (R1.4) the objects that belong to a particular set, or determine the sets a particular object belongs to.

R2: Managing actions

Managing actions consists in specifying their nature (e.g. by clicking on an 'alignment" icon, or a menu) (R2.1), specifying their parameters ("vertical" or "horizontal") (R2.2), perceiving their consequences (R2.3), and specifying the scope (R.2.4). Perceiving the consequences with appropriate feedback enables the user to realize the effects of its action after it is triggered [START_REF] Shneiderman | Direct manipulation: a step beyond programming languages[END_REF], and even before it is triggered.

R3: Fostering exploratory design

In order to support exploratory design efficiently, it is important to provide the user with tools that enable her to try (R3.1) and evaluate (R3.2) solutions during short-term exploration (R3.3), and compare (R3.4) different versions during middle-term exploration (R3.5) [START_REF] Terry | Recognizing creative needs in user interface design[END_REF]. When satisfied with the results, the user must be able to extend the modifications to other objects. If the system does not support this task efficiently, the user will have to repeat the same actions to propagate changes (viscosity). Finally, if structuring is a solution to the viscosity problem, it is a hurdle to exploration if required a priori. Therefore, structuring should be made a posteriori (R3.6) i.e. when actions have already been done.

INTERACTIVE TOOLS

We have explored a number of interaction techniques in order to provide the user with structure-based interactions. To design them, we have used traditional participatory design process with the users we interviewed. We have conducted ideation and prototyping sessions to fix the problem illustrated in the work scenarios, and to offer new ways of interacting with multiple objects. In the following, we present the tools and their usage that we designed.

Overview

To illustrate the interactive tools, we have designed a graphical drawing application. There are four parts: the tool palette on the left side, the workspace in the middle, the sample panel on the top right corner, and a property sheet on the bottom right corner (see Figure 5).

The workspace is the main view, where users can create a new object, by clicking and resizing. Selection is performed by clicking on an object or by drawing a rubber rectangle to encompass several items at once, as done with usual graphics editors. Selected items are highlighted with a shadow, while other items are made translucent. The samples panel contains a set of values for shape (square, oval, T for text), fill color (represented by a colored square), stroke color (stroked-only colored square) and stroke thickness (stroked-only circle). In order to modify a property of an object in the main view, users can drag a sample and drop it onto the object. Feedback is shown as soon as the sample hovers over the object, in order for the user to understand the action, and to assess the change before effectively applying it by releasing the mouse button. This enables the user to cancel the action, by releasing the button outside of any object (R3.1 try, R3.2 evaluate, R3.3 short term, R3.4 compare, R2.3 perceiving consequences). Drag and dropping samples also applies to a selection with multiple objects. The interactions described so far are not new. Next section presents the property sheet with novel interactions.

Implicit structure: an enhanced property sheet

A property sheet (or property box) is a window containing a vertical list of pairs of property type and value (e.g. shape: rectangle, color: green, thickness: 3…). A property sheet offers two services to the user: visualizing values (with progressive disclosure [START_REF] Johnson | The Xerox Star: A retrospective[END_REF]), and modifying them [START_REF] Johnson | The Xerox Star: A retrospective[END_REF]. With classical property sheets, if multiple objects are selected, only "shared values" (i.e. values shared by all objects) are shown and are modifiable (see Figure 6, left). Users can change a shared value for a property type, and the system reflects changes to all selected objects (power of action). Other properties, those that are multi-valuated, still appear, but with a blank fill. Those blank fills do not inform users with the values and cannot be modified.

Our version of the property sheet differs in that it shows all values for a multi-valuated property (see Figure 6, right), instead of displaying blank. This reveals an implicit structure of graphics, the sets of objects that share a graphical property. Though not explicitly defined by the user, we think that such sets may be useful, since users sometimes think about objects with a graphical predicate ("all red objects"). We relied on the display of those values to design a set of interactions that offer new services for exploratory design and structure-based interaction: query and selection of objects with graphic examples, selection refinement, properties modification on multiple objects with precision, and content correction. The representation of a shared value in the property sheet actually refers to two concepts: the value in itself, and the set of selected objects that exhibits this property value. As a value per se, and similarly to the interaction with the samples panel, users can drag the representation (considered as a value) from the property sheet onto (a selection of) objects in the main view to modify a property. If the shared value is numerical, users can hover over it and rotate the mouse wheel to increment or decrement it (power and precision). Together with immediate feedback, this enables both exploration and precise adjustment of properties, thus reducing temporal offset [START_REF] Beaudouin-Lafon | Instrumental Interaction: An Interaction Model for Designing Post-WIMP User Interfaces[END_REF] between action and reaction. Since the representation of a shared value also reifies [START_REF] Beaudouin-Lafon | Reification, polymorphism and reuse: three principles for designing visual interfaces[END_REF] a set of objects, hovering over a shared value highlights the concerned objects while blurring others (Figure 7). This makes it easy to figure out which set is made of what, and possibly detects outliers and correct them. In addition, users can drag a sample (hence a value) from the sample panels onto the representation of a shared value (considered as a set of objects) in the property sheet to modify at once one property of multiple objects (R2.4 scope) (Figure 8). Users can also drag a representation from (value) and in (set) the property sheet (Figure 9).

To select objects, users can directly click on them in the workspace, or draw a selection rectangle. In order to refine the selection, users can use three meta-instruments (i.e. instrument that control instrument, here the selection): Remover, Keeper and Extender. The interaction consists in a drag and drop of the representation of the instrument onto a shared value. Remover throws out of the selection all objects that have this shared value (Figure 10). Keeper keeps the objects that have this shared value in the selection, and throws away the others. Extender adds to the selection all objects that are not selected but possess this shared value. These interactions extend the set of example-based queries introduced above (R1.3 modify sets). The interaction to specify a dependency is as follows (Figure 11): by clicking on an object, users can toggle the display of the properties around it. They can press on a property, draw an elastic link, and drop it onto another object. The clone object appearance reflects immediately the appearance of the clone for that property. The interaction is coherent with the interaction between a sample of the property sheet and an object. As seen above, the management of any structure can be cumbersome. To minimize this aspect, our system proposes two ways of creating objects from others. Users can create a new object from a previous one, either by copying it, or by cloning it (R1.3 modify sets). Copying is the regular copy operation: properties from the copy are independent from the properties of the source. Cloning enables users to get a clone, whose properties are entirely delegated to the prototype (Figure 12). By creating a clone, users minimize the number of actions required to specify a single difference with the prototype: if they have copied instead of cloned, they would have to link all shared properties.

Choosing to clone or to copy may be premature at the moment of the creation of a new object from an existing one. To solve this problem, users can decide to change them to a copy or a clone after the creation of the object (R1.3 modify sets, R3.6 a posteriori structuring). This is made possible by tracing the history of objects, and how they were created. Toggling between copy and clone only affects the properties that were not set explicitly by the user (be it a value or a delegation).

Figure 13: The fill property is dragged on a shared value to specify that the fill property of a set of objects depends on the prototype (left).

When users find out that an object could be used as a prototype, one problem is to interact with similar objects in other to make them depend on the new prototype. A viscous solution would be to interact with each object and making it a clone of the prototype. A more efficient solution consists in selecting the objects that are be clones, and drop the property of the prototypes onto an object of the selection (R1.3 modify sets, R3.6 a posteriori structuring). To increase efficiency and integration, we have leveraged off the property sheet: the interaction consists in dropping the property onto a shared value, or the name of the property (Figure 13).

DISCUSSION

Comparison with CIS

CIS proposes two dimensions of analysis related to our problem: fusion and development. Fusion is related to the modification of several objects at once, and development is related to supporting the user in creating her own tools. However, we think that those two dimensions are not sufficient to express all concepts underlying actions on multiple objects at once.

Comparison with the delegation programming model

The property delegation graph is an extension of the delegation tree found in prototype-based languages [START_REF] Lieberman | Using prototypical objects to implement shared behavior in object-oriented systems[END_REF]. In a prototype tree, each node is linked to a prototype (a parent in the tree). A child can delegate the value of a property to its prototype. When drawing an object, the delegation algorithm checks whether a property is specified for a particular node. If not, the algorithm follows recursively the prototype branch, until the property is specified in an ancestor, and uses the value of that property for drawing.

With a tree, objects cannot have multiple parents. For example, the scene tree available in illustrator may be helpful to conceptualize the scene, but is unable to help specify cross-branches relationships. Conversely to a tree, a node in our graph of properties can have multiple parents. This enables users to be more specific about the parent that holds a particular property. Hence, a node can delegate the fill property to a prototype A, and the stroke-width property to a prototype B.

Drawbacks of the current design

The prototypes we have explored are far from being perfect. Even if we have crafted the interactions carefully so as to make them coherent and integrated as much as possible, we had to make compromise.

More work needs to done with respect to scalability. For example, the property sheet is not able to handle numerous shared values. A solution would be to provide a progressive disclosure of shared values, e.g. with scrollbars. The prototype/clone view also needs more work: if the links are numerous, the scene may result in a mess of tangled links. Again, progressive disclosure is a possible solution. We are also exploring other representations and interactions from the information visualization field. Some interactions need to be complemented. For example, the system does not check for cycle when the user tries to link two properties. Together with forbidding, appropriate feedback is necessary, such as displaying the links to show the cycle when hovering over a property. Furthermore, even if we designed them during participatory sessions with actual users, we did not evaluate them. In particular, we did not work on the discoverability of the interface: for example, there may be some concerns about the fact that users will not use shared values, either because shared values do not afford dropping samples on them, or because they are too complicated to understand.

CONCLUSION

In this paper, we have tackled the problem of the interaction with structures, and the interaction with content through structures. We have illustrated its importance in scenarios based on contextual inquiries, and showed that it underlies a number of past work. We have identified a set of requirements for the management of structures of interactive graphics, and the use of structures to act on the content. Based on the requirements, we have explored a set of interactions that provide partial solutions to the requirements: an enhanced property sheet, and a propertydelegation graph, together with coherent and wellintegrated interactions.

The examples we have shown involve drawing editors. However, this work also applies to any editor that uses graphics to display information, rather than creating them. For example, managing a calendar can benefit from the interaction we have designed: setting a particular duration or location to a set of entries, setting a location known one week after a set of meetings were scheduled, changing the title of entries that occur every Monday etc.

Our design aimed at illustrating the requirements and possible solutions, but other designs are possible. Though we think that structuring is important, we do not know yet how users actually benefit from it. During the evaluation of CIS, their authors witness that users were able to optimize their use of an interaction technique, and to adapt it to the current context [START_REF] Appert | Context matters: Evaluating Interaction Techniques with the CIS Model[END_REF]. We plan to design experiments that aim at assessing the usefulness of structuring, and to what extent it can support exploratory design.

Figure 1 :

 1 Figure 1: The user creates a key, and duplicates it.

Figure 2 :

 2 Figure 2: The text of the ʻI' key is not centered.

Figure 3 :

 3 Figure 3: A paper strip.

Figure 4 :

 4 Figure 4: Two versions of a strip board.

Figure 5 :

 5 Figure 5: Overview of the application. The workspace is at the center, the samples at the top right and the property sheet at the bottom right.

Figure 6 :

 6 Figure 6: The user's selection contains objects with varying shapes, fill colors, width, and height. A classical property sheet (left) displays a blank fill for those properties, whereas our property sheet (at right) displays all different values.

Figure 7 :

 7 Figure 7: The user's cursor is over the blue shared value of the fill property (fill: blue). Because they don't have this shared value, the green rectangle, the pink circle and the two yellow shapes are dimmed

Figure 9 :

 9 Figure 9: The user drags the "width: 280" shared value and drops it on the "shape: circle" shared value. All circles in the selection now have a width set to 280.

Figure 10 :

 10 Figure 10: The user drags the Remove instrument and drops it on the blue fill shared value. All blue objects are removed from the selection.

Figure 11 :

 11 Figure 11: The user draws a link between the Fill property into an object to specify a dependency Explicit structure: the property delegation graphBesides the augmented property sheet, we have explored an interactive tool that enables users to structure the content explicitly. Users can specify that the property of an object (the clone) depend on the property of another object (the prototype). A prototype plays the role of the master in Sketchpad: when users change a property of a prototype by dropping a sample from the property sheet onto the prototype, all dependent clones are changed accordingly (R2.4 scope, R1.3 modify sets).

Figure 12 :

 12 Figure 12: A prototype (left), and a clone (right)

ACKNOWLEDGMENTS

The authors would like to acknowledge colleagues.


Keywords: Urban lake, cyanobacteria modelling, hydrologic watershed modelling, high frequency measurements

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Modelling cyanobacteria dynamics in urban lakes: an integrated approach including watershed hydrologic modelling and high frequency data collection

Talita Silva, Brigitte Vinçon-Leite, Bruno J. Lemaire, Bruno Tassin, Nilo

Nascimento

To cite this version:

Talita Silva, Brigitte Vinçon-Leite, Bruno J. Lemaire, Bruno Tassin, Nilo Nascimento. Modelling cyanobacteria dynamics in urban lakes: an integrated approach including watershed hydrologic modelling and high frequency data collection. 11th edition of the World Wide Workshop for Young Environmental Scientists (WWW-YES-2011) -Urban Waters: resource or risks?, Jun 2011, Arcueil, France. hal-00607941

Modelling cyanobacteria dynamics in urban lakes: an integrated approach including watershed hydrologic modelling and high frequency data collection

Talita SILVA*, Brigitte VINÇON-LEITE*, Bruno J. LEMAIRE*, Bruno TASSIN* and Nilo NASCIMENTO**

INTRODUCTION

Urban lakes are frequently man-made, small and shallow water bodies, highly influenced by land-use changes in their watersheds and by urban stress such as industry, traffic, waste and drainage systems (Friese et al., 2010;Meyer and Likens, 2009). Worldwide, ponds and lakes located in urban regions performed several essential functions for the sustainable functioning of cities: storing rainwater; providing suitable aquatic and terrestrial habitats for a variety of wildlife; providing sport and recreation spaces; performing amenity and aesthetics function and often representing true heritage values. In addition, if examined within the context of global climate changes, these water bodies help to reduce the extremes of atmospheric temperature in the cities (Spronken-Smith & Oke 1999).

Despite the importance of small shallow lakes in urban centres, research has mainly focused on large and deep lakes (Scheffer 1998). Only recently, as the ability of urban aquatic ecosystems to provide services that benefit humans has been reduced, restoration projects have begun in many cities, supported by scientific studies that aim to investigate urbanization impacts in lake functioning (Stoianov et al. 2000, Havens et al. 2001, Ruley & Rusch 2004, Meyer & Likens 2009). Furthermore, only recent studies have taken into account the impacts on urban aquatic ecosystems caused by global changes as climate change (Trolle et al. 2010).

Meteorological forcing governs many of the physical aspects of lake ecosystems (e.g. lake temperature and its stratification) which affect the physiology, life story and development of phytoplankton and fish communities (Blenckner et al. 2007). Phytoplankton communities, especially cyanobacteria, play a key role in urban aquatic environments since they are potential producers of toxic substances, which disrupt water uses and cause health problems (Huisman et al. 2005). The effects of climate change on the physical and ecological dynamics in lakes can be diverse, and individual lakes may respond very differently to changes in climate (Mooij et al., 2005;Tanentzap et al., 2008). Although, it is generally expected that global warming will increase productivity in most lakes and favour cyanobacteria blooms by (Paerl & Huisman 2008): (1) rising water temperature, since cyanobacteria normally growth better at high temperature than other phytoplankton species;

(2) lengthening optimal growth periods, it means, earlier stratification in spring and later destratification in autumn;

(3) affecting patterns of precipitation and drought which can intensify surface and groundwater nutrient discharge into water bodies and increase water residence time.

On the other hand, growth in population and urbanization has intensified exchange of nitrogen and phosphorous between lands and surface water, which increases the intake of nutrients in aquatic environments and contributes to accelerate their eutrophication (Meyer and Likens, 2009). Increasing impervious area in the catchment basin raises runoff in volume and speed, causing greater carrying capacity and greater nutrient load to aquatic receptors. This excessively availability of nutrients results in unnatural high primary productivity and phytoplankton blooms can be expected. In urban regions, nutrient load traditionally comes from two sources: point sources, as municipal and industrial wastewater and; non-point sources, as atmospheric deposition and drainage water. Point loadings are usually easy to determinate, since they do not depend on stochastic process like precipitation and temperature. By contrast, non-point loadings are difficult to estimate accurately due to the stochastic hydro-chemical processes and the heterogeneous of soil properties and vegetation (Nikolaidis et al., 1998).

Problem statement. In order to define more appropriate strategies to restore the water quality in urban lakes, deeper understand of the links between the lake ecological functioning and its watershed is needed. Furthermore, the impacts of the urbanization expansion and the climate change in the water quality should be taken into account in the management strategies of these lakes and their watersheds. Modelling approaches are useful tools to better understand phenomena occurring into the lakes and to estimate their response to different environmental management strategies or to different watershed changes, such as land-uses changes, increase of the impervious area or improvements in the sanitation system.

This paper describes the first steps of a PhD research project that aims to evaluate the impacts of watershed changes on cyanobacterial dynamic in urban lakes using modelling approach and high frequency data. The main objectives of this paper are: (1) to assess the performance of an existing lake ecological model to simulate cyanobacteria dynamics in urban lakes using high frequency data as input;

(2) to propose an integrated modelling approach, it means, a methodology for linking a hydrological watershed model and a lake ecosystem model. The first objective was achieved using data from Lake Enghien-les-Bains, France. The second objective was proposed to Lake Pampulha, Brazil, and its watershed. Thus, the methods and results sections of this paper are divided in two different parts: part I concerns the lake ecological model applied to the French study site and part II deals with the integrated modelling approach of the Brazilian lake.

METHODS

Part I -Lake ecological model

In limnology modelling, quite frequently, hydrodynamics models are coupled to water quality ecological models: the former take into account physical processes of transport and mixing in the water column, while the latter are responsible for representing the main chemical and biological processes that affect phytoplankton and higher trophic levels (Hamilton and Schladow, 1997). This type of coupled model was used in this study in order to simulate cyanobacteria dynamics in Lake Enghien-les-Bains.

Study site. Lake Enghien-les-Bains is located in France (Val-d'Oise), 11 km north of Paris (48°58'N, 2°18'E, see Figure 1). It is a small and shallow urban lake that plays a significant role in the stormwater management of its watershed by storing up to 100,000 m 3 of rainwater. The main physical characteristics of the water body and its watershed are listed in Table 1. Besides rainwater, the lake receives wastewater discharges from inappropriate connections in the stormwater network, resulting in water quality deterioration. According to Quiblier et al. (2008), water quality monitoring revealed that Lake Enghien is affected by blooms of Planktothrix agardhii, chlorophyll-a concentration (below chl-a) exceeding 350 μg chl-a.L -1 in midsummer (50 μg chl-a.L -1 is the threshold recommended by WHO for swimming prohibition). , 1997). The input data required to DYCD are: initial conditions for cyanobacteria biomass, nutrient concentrations, dissolved oxygen and water temperature; lake morphometry; inflows (including inflow water quality); outflows and; meteorological forcing. The latter is represented by wind speed, air temperature, solar radiation, rainfall, cloud cover and vapour pressure (see Figure 3). Data collection. Most data necessary to run DYCD were obtained from a freshwater-adapted measurement buoy installed on the lake in November 2008 within the PROLIPHYC research project (Monitoring system of phytoplankton blooms -application to cyanobacteria, funded by the French National Agency for Research, ANR-PRECODD). This buoy was equipped with meteorological sensors and immersed probes for measuring water quality parameters such as dissolved oxygen, water temperature, pH, conductivity and chl-a. The latter corresponds to the total chl-a and the chl-a related to four different groups of phytoplankton: cyanobacteria, chlorophyta, diatoms and cryptophyta. The measurements were performed in every 30 min at a depth varying from 0.50 to 1.0 m (for water parameters) and daily transmitted through GPRS protocol to a database. More technical details about measurement buoy sensors and probes are described in Silva (2010).

Modelling approach. DYRESM was coupled to CAEDYM in order to simulate only cyanobacteria, the dominant phytoplankton group throughout the year 2009. DYCD has been successfully applied and validated since its development in many lakes/reservoirs around the world (Gilboa et al., 2009;Hornung, 2002;McDonald and Urban, 2010), however, as far as we are aware, DYCD has been employed only in multi-year simulations (3 to 20 or more years) to provide means of predicting seasonal and inter-annual variability of lakes. In this paper, DYCD was used to simulate cyanobacteria dynamics throughout short time intervals (about 15 days).

Part II -Integrated modelling approach

The methodology applied to implement the integrated modelling approach in Lake Pampulha is described below. The few data available for Lake Enghien watershed do not allow us to use this modelling approach in the French study site. Instead, in Lake Pampulha, a complete data set will be available from 2012, since its watershed will be equipped with rain gauges, flow rate sensors and automatic samplers. Furthermore, Lake Pampulha catchment is located in a peri-urban area with a potential for urban expansion greater than Lake Enghien catchment. The latter is located in an urban region already highly densified and hence, few changes in the watershed are expected for the next years.

Study site. Pampulha dam (also called Lake Pampulha) is an artificial lake located in northeastern part of Belo Horizonte city in Brazil (19°55'S, 43°56'W, see Figure 2). The main physical characteristics of Lake Pampulha and its watershed are listed in Table 2. Lake Pampulha is fed by eight small streams (Figure 2), Sarandi and Ressaca streams being the most important (70% of the total water income in the reservoir) and also the most polluted (Friese et al., 2010). Originally, Lake Pampulha was built to supply drinking water to the city, however, since the 70s, the water quality has been impaired as consequence of the rapid watershed urbanization with neither sanitation infrastructure nor erosion control. Nowadays, lake silting and reduction of its storage capacity, water eutrophication, cyanobacterial blooms and excessive growth of macrophytes are the main problems to be faced in Lake Pampulha. Despite the degraded water quality, Lake Pampulha is an important tourist hot spot and it helps in flood control by storing rainwater. The municipality of Belo Horizonte is very interested in improving the lake water quality, so it could be used to recreational and sportive activities.

Integrated modelling approach. DYCD will be used on Lake Pampulha whose catchment area runoff will be simulated by a hydrological model. The results of the latter will be used to input inflow rate and quality into the lake model (Figure 3). Obviously, DYCD could be fed directly by inflow measurements of the tributaries, instead of simulated inflow; however, the purpose of this integrated approach is to help in predicting the impacts of watershed changes on lake ecosystems. Therefore, a hydrological watershed model that takes into account catchment characteristics such as land-uses and impervious area rate is necessary to simulate runoff of future scenarios representing watershed evolution.

Watershed hydrological model. For the moment, the choice of the hydrological watershed model to be applied in the integrated modelling approach is ongoing. In general, hydrological models are dynamic rainfall-runoff models which compute flows and non-point source nutrients from watershed runoff. The processes taken into account in this type of model are described as follows (Figure 3): (1) during dry periods, pollutants are deposited over the land surface (2) during rain events, rain falls over the catchment area and washes off pollutants; (3) according to the characteristics of the catchment area (e.g. imperviousness, slope), it generates outflows in form of infiltration to the groundwater and/or in form of surface runoff; (4) this runoff and part of the groundwater reach the stormwater network and are drained to an outfall, Lake Pampulha, in our case (Rossman, 2010). Concluding, the hydrological watershed model will use rainfall data, catchment and stormwater network characteristics to simulate the quantity and quality of the runoff produced in the Lake Pampulha watershed. Data collection. A measurement buoy similar to this one used in Lake Enghien will be installed on Lake Pampulha for monitoring water quality parameters every 30 min: temperature, conductivity, pH, dissolved oxygen and chl-a. Meteorological data at hourly time step will be provided by the Brazilian National Institute of Meteorology, INMET. Concerning the watershed, the municipality of Belo Horizonte will implement on the two main tributaries of Lake Pampulha (streams Ressaca and Sarandi) and its outlet (stream Pampulha) measurement stations equipped with level sensors and rain gauges. Within MAPLU 2 research project (Storm water management project, funded by the Brazilian Agency for Funding Study and Projects -FINEP), probes to measure at high frequency (5 min) flow, temperature, conductivity and turbidity of the streams will be installed on the same stations mentioned above, as well as automatic samplers to collect water for laboratorial analysis (BOD, TSS, VSS, NTK, NO 3 -, P tot , PO 4 -3 , metals and hydrocarbons). Data set will be obtained over two hydrological cycles, from 2012 to 2013.

RESULTS

Part I -Lake ecological model

Results. The thermal and ecological model was manually calibrated from 1 st to 16 th June 2009, period corresponding to the first cyanobacterial bloom of the year. The calibrated model was then applied to simulate the period from 3 rd to 18 th July 2009, in which cyanobacteria chl-a concentration reaches its maximum value over the year (358 μg chl-a.L -1 ). Model results for calibration and validation simulations show good agreement with measurements ( Figure 4). The goodness of fit is assessed through the correlation coefficient (r) and the root mean square error (RMSE). Water temperature evolution during the two periods is successfully described by the model, respectively r = 0.91; RMSE = 0.98°C and r = 0.95, RMSE = 0.65°C. Cyanobacteria dynamics is also well captured by the model (r = 0.97; RMSE = 15.8 µg chl-a.L -1 and r = 0.71; RMSE = 25.7µg chl-a.L -1 ). The high frequency of data acquisition provides a very rigorous assessment of model performance since its results were compared with buoy measurements at hourly time-step. Comparing the results of this modelling with other lake studies carried out with DYCD supports this assertion (Burger et al., 2008;Gal et al., 2009). DYCD model can be considered validated for simulating cyanobacteria dynamics in a shallow urban lake, for short-term simulations (few weeks).

Part II -Integrated modelling approach

Expected results. The installation of the water quality monitoring devices in Lake Pampulha and in its watershed is being carried out throughout 2011. The first data needed to input the models will be available from the beginning of 2012. Once calibrated and validated, the hydrological watershed model and the lake ecological model will allow us to better understand the factors controlling cyanobacteria dynamic and its link with the watershed. Furthermore, both models will be used to propose different scenarios of watershed evolution: on the one hand, meteorological changes such as increasing in air temperature and changes in rainfall regime; on the other hand, intensification of land-use and expansion of impervious area leading to an increasing of the external loading of nutrients into the lake. Improvements in the sanitary system of the watershed will be also taken into account, since they can result in a decrease of external nutrient loading into the lake. Thus, lake response to these different scenarios will be simulated thanks to this integrated approach. Research with similar goals have already been undertaken (Hornung, 2002;Trolle et al., 2010), however, as far as we are aware, high frequency data were not used until now. Thus, we hope that the continuous high frequency monitoring adopted in our approach will improve the accuracy of the models and provide hitherto temporal resolution of phenomena occurring into the lake.

CONCLUSIONS

Water bodies inserted in urban areas represent a key role to overcome the challenge of the coming decades in urban centres: harmonize economic growth, social development, biodiversity conservation and preservation of ecosystems. Water managers need to take into account the effects of watershed changes and climate change in their strategies to restore lake water quality.

Our results on cyanobacteria modelling in Lake Enghien show the reliability of the ecological model whose performance has been thoroughly assessed against high-frequency data. The integrated approach linking a watershed hydrological model and a cyanobacteria dynamics model in Lake Pampulha may not only help to guide its restoration and preservation, but also that of other water bodies in developing urban areas. Finally, building scenarios to represent watershed evolution and simulating the lake response will highlight the processes the most likely to be affected by changes, and therefore support stakeholders' decisions. Predicting the effects of climate change on trophic status of three morphologically varying lakes: Implications for lake restoration and management. Environmental Modelling & Software, 26(4), 354-370. -2011-Silva-Paper-2011-07-01.doc

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  Deterministic model. For simulating cyanobacteria dynamics in Lake Enghien, the deterministic model DYRESM-CAEDYM (below DYCD) was used. This model was developed by the Centre for Water Research at University of Western Australia. DYRESM (DYnamic REServoir Simulation Model) is a one-dimensional hydrodynamics model for predicting the vertical distribution of temperature, salinity and density in lakes and reservoirs. DYRESM can run either in isolation for purely hydrodynamics studies or coupled to CAEDYM (Computational Aquatic Ecosystem Dynamics Model), for investigations involving biological and/or chemical processes normally associated with water quality such as nutrient cycling studies; algal succession studies; food-web investigations; pathogen dynamics investigations; suspended solids studies; and toxic metal studies (Hamilton and Schladow

Figure 1 .

 1 Figure 1. Lake Enghien-les-Bains location (Enghien-les-Bains city, France) and its urbanized surrounding.

Figure 2 :

 2 Figure 2: Lake Pampulha location and its watershed (Resck et al., 2007). Tributaries: (1) Olhos d'Agua; (2) AABB; (3) Braunas; (4) Agua Funda; (5) Sarandi; (6) Ressaca; (7) Tijuco and; (8) Mergulhão. Outlet: (9) Pampulha.

Figure 3 :

 3 Figure 3: Integrated modelling approach diagram: (a) hydrological watershed model type and the process taken into account to compute runoff from the catchment area (model output) using precipitation and catchment characteristics (model inputs). (b) DYCD inputs and output. The link between the models is held by the inflow data which are simultaneously an output from the hydrological model and an input to DYCD.

Figure 4 :

 4 Figure 4: Simulated (lines) and buoy measures (dots) for water temperature (a, b) and cyanobacteria chl-a concentration (c, d). Simulation period: 1 st to 16 th June (a, c) and 3 rd to18 th July (b, d).

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  QUIBLIER C. et al. (2008). Rapport de pré-implantation de la bouée Proliphyc sur le Lac d'Enghien-les-Bains, Report 3.1.1 • RESCK R.P., Bezerra Neto J.F and Mota Coellho R.M.(2007). Nova Batimetria a avaliação de parâmetros morfométricos da Lagoa da Pampulha (Belo Horizonte, Brasil) Geografias artigos cientificos, 3(2), 24-37. • ROSSMAN L. A. (2010). Storm Water Management Model. User's Manual, version 5.0. U.S. EPA, Water Supply and Water Resources Division, National Risk Management Research Laboratory, Cincinnati (USA), 295. • RULEY J. E. and Rusch K. A. (2004). Development of a simplified phosphorus management model for a shallow, subtropical, urban hypereutrophic lake. Ecological Engineering, 22 (2), 77-98. • SCHEFFER M. (1998). Ecology of shallow lakes. Population and community biology series 22. Kluwer Academic Publishers, Netherlands: 315. • SILVA T. (2010). Modélisation des efflorescences de phytoplancton dans les lacs urbains. Application aux cyanobactéries du lac d'Enghien-les-Bains. Laboratoire Eau Environnement et Systèmes Urbains Master. Ecole Nationale des Ponts ParisTech, France (Champs-sur-Marne). • SPRONKEN-SMITH, R.A. & T.R. Oke. 1999. Scale Modelling of Nocturnal Cooling in Urban Parks. Boundary-Layer Meteorology 93. • STOIANOV I., Chapra S., Maksimovic C. (2000). A framework linking urban park land use with pond water quality. Urban Water, 2, 47-62. • TANENTZAP A. J. et al. (2008). Cooling lakes while the world warms: Effects of forest regrowth and increased dissolved organic matter on the thermal regime of a temperate, urban lake. Limnology and Oceanography, 53(1), 404-410. • TROLLE D., Hamilton D. P., Pilditch C. A., Duggan I. C. and Jeppesen E. (2010).

Table 1 . Main physical characteristics of Lake Enghien-les-Bains

 1

		Lake					Watershed
	Mean depth Max. depth	Area	Volume		Area		Population
	1.3 m	2.65 m	41 ha 534,000 m	3	54 km	2	~200,000 inh.

Table 2 . Main physical characteristics of Lake Pampulha

 2

		Lake				Watershed
	Mean depth Max. depth	Area	Volume	Area	Population
	5.1 m	16.2 m	197 ha 10 x 10	6 m

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~350,000 inh. 11th WWW YES, Arcueil, France, 6 -10 June 2011 Silva et al.