Mining effective design solutions based on a model-driven approach

Transcription

1 ata Mining VI 463 Mining effetive design solutions based on a model-driven approah T. Katsimpa 2, S. Sirmakessis 1,. Tsakalidis 1,2 & G. Tzimas 1,2 1 Researh ademi omputer Tehnology Institute, Hellas 2 omputer Engineering & Informatis epartment, University of Patras, Hellas bstrat The World Wide Web evolution has posed new hallenges for Web appliation developers. Today s Web appliations present their ontent in a dynami manner, allow users to interat with them at a high level of sophistiation, and manage huge amounts of data, leading to a high degree of omplexity. To ope with this emerging problem, a variety of modeling methodologies, web design patterns and tehniques have been introdued. In this work we propose a methodology for mining and evaluating reurrent design solutions in the oneptual shema of Web appliations modeled using WebML, a modeling language for designing data-intensive appliations. Identifying effetive design solutions may lead to an effiient deployment of reuse. By means of our approah, an extension of the predefined set of patterns supported by WebML an be realized. What is more, when applying the methodology in a large number of appliations of the same domain, templates for Web appliation frameworks an be identified. Keywords: reuse, web modelling, web design patterns, model mining. 1 Introdution Nowadays, the design, development and maintenane of Web appliations have beome some of the most hallenging problems that web arhitets have to fae. Modern Web appliations are ompletely different in omparison to the traditional Web sites whih provide only stati ontent. They are required to manage huge amounts of data, exeute various omplex funtions and deliver their ontent in a variety of forms, aording to the user profile or role and aording to the media with whih the user aesses the appliation. WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

2 464 ata Mining VI In order to provide means for the effetive design and deployment of Web appliations, several methodologies and tehniques have been proposed by the researh ommunity. These methodologies, Retshitzegger and Shwinger [1], elevate the level of abstration in the design proess, provide tehnology independent design solutions and are based on the idea of separation of onerns. They inorporate different models for data management, navigation struture and presentation of pages to the end-users. HM was the first methodology to introdue the model-driven approah in the area of hypermedia design and was followed by RMM. Later, based on the HM a number of modelling methodologies were introdued mainly fousing on Web ppliation design, suh as HM-Lite, Strudel and OOHM. raneus is a proposal for web design and reverse engineering. Extensions of the UML language so as to make it suitable to model Web appliations have been proposed by onallen. Finally, a new modelling language was introdued, the Web modelling language WebML, whih is destined to speify omplex Web appliations at the oneptual level and along several dimensions. The methodologies noted above provide a onrete framework for Web appliation design, elevating the effiieny in the design proess and providing a firm basis for re-engineering and maintenane of web appliations. Utilizing previous experiene an also boost the final appliation s quality. To this end, the notion of design patterns was first introdued in the field of ivil engineering, lexander et al. [2] and now has expanded to a diversity of domains, inluding software engineering and in partiular Web engineering. esign patterns represent design knowledge ulled from the solutions given by experiened designers that have enountered these same problems before, possibly with slight variations Shwabe et al. [3]. By using patterns, the web arhitet onstruts appliations starting from ustomizable omponents, rather than from srath, and enfores a oherent design style over large and ompliated appliations, augmenting hypertext regularity and usability. Taking the use of design patterns one step further, the notion of Web appliation frameworks for speifi domains was introdued [3,4]. lthough the use of web design patterns is valuable when building a web appliation, omplex Web appliations need to maximize reusing larger design strutures (the whole navigation topology or struture plus assoiated funtionality). These design strutures may arise at the appliation (oneptual level) or during navigational design. esigners should find ways to express these ommonalities by using generi designs suh that only aspets unique to a partiular site should be designed or programmed. Web appliation frameworks apture the design deisions that are ommon to a ategory of Web sites and provide reusable design for that ategory eri et al. [4]. From the above, the need and importane to identify reusable design solutions is rather obvious. The ontribution of this paper is the provision of a mehanism, whih mines and evaluates reusable design solutions at the oneptual shema of a Web appliation built using WebML. Moreover, applying the proposed mehanism in a number of Web appliations of the same domain, Web appliation frameworks an be identified. In this work, WebML has been utilized WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

3 ata Mining VI 465 as design platform for the methods proposed, mainly due to its robustness and the fat that it is supported by an effiient ase tool alled WebRatio [5]. Most of the work presented here an be generalized and applied to appliations utilizing other modeling languages with slight straightforward modifiations. The remainder of this paper is organized as follows: Setion 2 presents some bakground onepts referring to the WebML method. Setion 3 provides a motivating example, while setion 4 desribes our methodology to mine reusable design solutions at the oneptual shema of Web appliations. Setion 5 illustrates a quality evaluation mehanism for the solutions retrieved by means of onsisteny. Finally, setion 6 draws our onlusions. 2 WebML at a glane Before proeeding to the rest of the paper, it is important to provide a quik overview of the WebML ore onepts. WebML is a notation for speifying omplex Web sites and appliations at the oneptual level eri et al. [6]. WebML onsists of the ata Model and the Hypertext Model. The data model utilizes the well known E/R model, in order to organize the ontent of the appliation. The hypertext model desribes how data obets are assembled into information units and elements and the way these elements are onneted by links to form hypertexts. ifferent hypertexts, alled site views, that support different user profiles, an be reated among the same data model. Site views are graphs of pages, whih are the atual ontainers of information and are built of ontent units. Units represent atomi piees of information to be published; a unit seletor speifies a prediate identifying the data to be extrated from the underlying database and displayed by the unit. Pages and units an be linked in a variety of onfigurations by means of links to form a hypertext. Besides representing user navigation, links between units also speify the transfer of ertain information (alled ontext) that the destination unit uses for seleting the data instanes to be displayed. Finally, the exeution of arbitrary business ations is modeled by means of operation units. n operation unit an be linked to other operations or ontent units. WebML inorporates some predefined operations for reating, modifying and deleting the instanes of entities and relationships, and allows developers to extend this set with their own operations. Table 1: Some basi WebML units. ata unit Multidata unit Index unit HierarhialIndex Entry unit Entity [Seletor] It displays a set of attributes for a single entity instane. Entity [Seletor] It displays a set of instanes for a given entity. Entity [Seletor] It displays a list of properties, of a given set of entity instanes. Entity1 [Seletor1] NEST Entity2 [Seletor2] It displays index entries organized in a multi-level tree. It represents forms for olleting input data into fields. WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

4 466 ata Mining VI WebML aknowledging the importane of design patterns has defined a primitive set of design patterns, offering proved solutions to problems ourring in real-life appliations. ording to the role information obets play in the appliation, four lasses of obets have been identified (ore and interonnetion onepts, aess failitators, personalization obets), that an be organized in a variety of ways to onstrut sub-shemas eri et al. [7]. The organization of ontent in web pages an also be simplified by making use of design patterns. Reurrent navigation hains of unit ompositions for ontent publishing (asaded index, indexed guided tour, obet viewpoint et.), as well as patterns for ontent management operations (obet reation-deletionmodifiation, asaded delete et.) have been identified eri et al.[6]. pattern in WebML, typially onsists of a ore speifiation, representing the invariant WebML unit omposition that haraterizes the pattern, and a number of pattern variants, whih extend the ore speifiation with all the valid modalities in whih the pattern an start (starting variants) or terminate (termination variants). Starting and termination variants respetively desribe whih units an be used for passing the ontext to the ore pattern and how the ontext generated by the ore pattern is passed to suessive ompositions in the hypertext Fraternali et al. [8]. WebML, furthermore, separating the various appliations aording to their information-delivery mission, has identified skeletons and WebML appliation frameworks eri et al. [4] that an be applied and used to Web appliations, depending on their funtionalities. 3 Motivating example In this setion we provide an instane of a WebML sheme modelling an e- learning senario that will serve as a running example throughout this paper. We assume that every lesson omprises of a number of letures, eah of whih ontains one more exerises. Eah lesson is supported by a forum, whih omprises of topis ontaining messages. The teahers and students are the basi groups of users that an aess this appliation, eah of whih has different permissions. The first part of figure 1 depits part of a teaher s site view. Suppose that the teaher wants to alter the ontents of an exerise. global parameter is used to hold the obet identifier, OI, of the teaher urrently logged into the Web appliation. Initially, the teaher views a hierarhial index of the lessons he teahes per ategory. The Lesson page ontains the Lesson data unit providing information about the lesson seleted and the LeturesIndex shows a list of the lesson s letures. Finally, the teaher, by seleting one of the letures, an aess the Exerises multidata unit, that displays all exerises related to this speifi leture. hoosing the desired exerise, he may modify its ontents. The seond part of the same figure depits part of a student s site view. Suppose that the student wants to view the messages of a lesson s forum. global parameter is used to hold the OI of the student urrently logged into the appliation. hierarhial index ontains a two-level hierarhy of lessons per ategory that the student attends. Seleting a lesson, he an view information related to it ( Lesson data unit). In the same page, the ForumsIndex displays WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

5 ata Mining VI 467 all the topis onerning the hosen lesson, whereas the Topi data unit displays information about a speifi topi. Finally, the Messages multidata unit shows the messages that belong to the seleted topi. The student an selet a message in order to view it in detail. Teaher s SV Student s SV Lesson Lesson Get Teaher Lesson LeturesIndex Get Student Lesson ForumsIndex userid ategory Nest Letures userid ategory Nest Topis Exerise ata Entry Exerise Letures Exerises Leture Message Message Topis Messages Topi Exerises KO Modify OK Exerises Letures Messages Messages Topis Exerises Figure 1: Teaher s and student s site views. 4 Methodologial approah In the sequel, we present in detail a methodology for mining reurrent design solutions in the WebML oneptual shemas of appliations. Our obetive is to apture ompositions of hypertext elements (pages, units, operations, links) serving several appliation purposes. These onfigurations are aptured in the proess of (or after) modelling a Web appliation, and an serve as effetive design solutions enabling reuse, onsisteny and quality improvement in the development and maintenane proess. 4.1 Initialisation In this phase we preproess the appliation s hypertext model, in order to form the basis for the model mining mehanism needed in the phases to follow. More preisely, onsidering an appliation having a number of site views we onvert every site view into a direted graph based on the notation desribed below, thus onstruting a set of graphs representing the navigation, ontent presentation and manipulation mehanisms of the appliation. We define a site view as a direted graph, G(V, E, f V, f E ), omprising of a set of nodes V, a set of edges E, a node-labeling funtion f V : V Σ V, and an edgelabeling funtion f E : E Σ E. f V assigns letters drawn from an alphabet Σ V to the site view nodes, whereas f E has the same role for links and the edge alphabet Σ E. Σ V has a different letter for eah different WebML element (ontent units, operations, pages et). orrespondingly, Σ E omprises of all the different kinds of links (ontextual, non ontextual et.). Besides the predefined WebML links, we introdue a speial kind of edge (labeled in the graph) in order to represent the ontainment of units or sub-pages in pages, as well as pages, sub- WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

6 468 ata Mining VI areas and units in areas (note that arbitrary ontainment sequenes an exist ). transformation example of the two site views desribed in setion 3 is depited in fig. 2. S S P P P P E P P P P N N G H I M G H I M Figure 2: Graph transformation of the two site views. 4.2 Extration of predefined patterns and uniformity We traverse iteratively eah graph onstruted in the previous phase in order to loate predefined ontent publishing and management WebML patterns taking into aount their variants. Every pattern found is stored in a pattern ourrenes repository, along with its starting and termination variants. The ourrene frequeny of eah pattern is also stored. The retrieval of a predefined pattern an be ahieved using graph mathing tools suh as GraphGrep [9], whih given a olletion of graphs and a sub-graph (in our ase, graphs representing the predefined patterns), returns all the ourrenes of the pattern in eah graph. Next, taking into aount the various WebML predefined variants we have loated, we substitute, where possible (this step requires the designer s intervention), the variants found within eah graph with the default pattern variant. The default pattern variant is the one having the maximum ourrene frequeny. Upon ompletion of this step, a more uniform definition of eah site view is aomplished, and new graphs representing the hypertext shema are generated. 4.3 esign solutions extration We traverse eah newly generated graph so as to identify idential subgraphs - andidate design solutions. lthough the problem is NP-omplete Garey and Johnson [10], this an be ahieved by utilizing several heuristi algorithms (e.g. losegraph Yan and Han [11]). These algorithms demand as input the dataset of graphs to be searhed and the desired support (the minimum perentage of ourrenes in the entire database) of the subgraphs to be retrieved. The extrated subgraphs should not represent predefined WebML patterns, but may ontain one or more of them. We store the mined subgraphs in the pattern ourrenes repository, along with their variants. For instane, omparing the graphs that orrespond to our example, an idential subgraph is easily identified. The entire student s graph onstitutes a subgraph of the teaher s graph and should be stored. The teaher s graph extends the identified andidate design solution with a subgraph that orresponds WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

7 ata Mining VI 469 to an obet modify pattern. Thus, a variant of the andidate design solution an be extrated from the teaher s graph, and should also be stored. fterwards, we examine the retrieved design solutions and substitute, where possible, the variants with the default onstrut variant, generating new graphs representing the hypertext shema of the appliation. The newly generated graphs are one again searhed for hypertext onfigurations that were not retrieved in the previous step. 4.4 Extending the sets of design solutions This phase aims at aquiring a larger number of andidate design solutions. First, we examine every solution stored in the repository, and in ase it ontains predefined WebML ontent management patterns, but one or more of the remaining patterns is/are missing, we add the respetive missing ones. For instane, if we loate a design onstrut, whose starting or termination variant is a reate pattern, we omplement it by adding the modify and/or delete pattern(s). In our example we retrieved a variant that ontains a modify obet pattern. Thus, more variants that ontain the obet deletion or reation pattern in plae of the obet modify pattern should be stored in the repository. The repository an be further extended with broader design solutions, if we take into aount the intermediate onstruts of units that may onnet two or more already mined design onstruts. Traversing the graphs, we searh for ouples of subgraphs (already mined design onfigurations) that are interonneted through different nodes or subgraphs. We query for interonnetion variants that are smaller than any other onfiguration involved in the larger design solution (fig. 3). Therefore, we utilize these onstruts that inlude, at most, the minimum number of units among the onfigurations involved. whole site view, in the worst ase, ould be thought of as a andidate design solution, but it will be disarded due to the evaluation metris of the following setion. esign onstrut i esign onstrut esign onstrut i esign onstrut E I S I N Intermediate Subgraph E E I S N H Intermediate Subgraph E Figure 3: Extending the set of design solutions. 4.5 Evaluation metris Up to this point, the repository may ontain a large number of andidate design solutions. This number may inrease even more, if we apply the methodology to omplex Web appliations or to a number of appliations. In order to deide whether the retrieved design onstruts an be onsidered as effetive design solutions, we have to evaluate them in terms of importane and propose a first level ranking. To this end several fators should be taken into aount. WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

8 470 ata Mining VI first ruial fator is the frequeny of appearane of a speifi design onstrut in the oneptual shema. High frequeny implies high probability of effetive use of a speifi navigational hain. We define as appearane f the frequeny of a design solution, whih omprises of: a) the overall number of appearing instanes of a design solution, f 0, b) the appearane in f a areas, ) the appearane in f σ site views, and d) the appearane in f π pages. The size of an extrated onfiguration an be also onsidered as a very important metri. It is obvious that repetition of a large design onfiguration in the hypertext model of an appliation implies a high probability for having identified the use of an important solution. Thus, we introdue population p, as the number of WebML elements involved in the onfiguration. Population depends on: a) p δ, the number of ontent units, b) p l, the number of links and ) p op, the number of operation units. ombining the frequeny and the population of a design solution, we ompute the importane V of a design solution utilizing the following formula: V = f x p (1) fo, fa, fσ, fπ, where f = + + +, f [0,4] (2) fo,max Nα Nσ Nπ f max represents the maximum value of the orresponding metri, while N is the orresponding sum of areas, site views and pages overall in a speifi WebML oneptual shema, and pδ, pl, pop, p = + +, p [0,3] (3) pδ,max pl,max pop,max nother fator that should be taken into aount is the omplexity d of a design onstrut, depending on the number of pages that host the onstrut (fragmentation φ). That is: d = 1/φ (4) Finally, we introdue the semanti value e of a design solution that represents the number of data model entities partiipating in the design solution onsidered per oneptual fator as: a) e, entities belonging to the ore subshema, b) e per, entities belonging to the personalization sub-shema and ) e a, entities belonging to the aess sub-shema. The value of e is alulated by: e, eper, ea, e = + +, e [0,3] (5) e,max eper,max ea,max ombining the above metris, the total impat I of a design solution in a WebML oneptual shema, is given by: e I = V (6) φ fter omputing the fator I for every design solution in a speifi oneptual shema, results are presented in a desending order to depit the most important and effetive design solutions on the top. The same proedure an be applied repeatedly to site views from different appliations in order to detet similar pattern implementation behaviours and group the results. WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

9 ata Mining VI 471 Having evaluated and ranked the various design onstruts; the hypertext arhitet has aess to a library of design solutions along with their variants. pplying the proposed mehanism in a number of appliations of the same domain, patterns and templates for Web appliation frameworks, supporting the appliations ommonalities and aommodating validations, an be identified. What is more, the designer s task an be further failitated; utilizing languages suh as transformers-by example Lehner and Shrefl [12] (a language whih allows defining transformers for WebML shemes by example). The identified frameworks, in ombination with transformers by example, assist the designer in performing effetive and onsistent modelling ativities in an automati manner and onstruting wizards for future web appliation development. 5 Quality evaluation The quality of the final appliation an benefit from the effiient adoption of suessful design solutions. Even when the web arhitet has effetive design solutions at his disposal, the problem that arises is that of verifying if they are applied onsistently throughout the appliation. If the design solutions are onsistently used, end-users find it easier to understand how to navigate through an appliation and how to ativate operations. Moreover, web arhitets an predit in advane how to organize an unfamiliar setion of the appliation. In Fraternali et al. [8] a methodology is introdued for the evaluation of the onsistent appliation of predefined WebML design patterns within the oneptual shema of an appliation. We utilize that methodology and extend it, in order to introdue metris depiting the onsistent appliation of the design solutions retrieved. In order to ahieve that, we introdue two metris that ompute the statistial variane of the ourrene of the N termination or starting variants of the onfigurations retrieved, normalized with respet to the best ase variane. The Start Point Metri (SPM) and the End Point Metri (EPM). The definition of SPM follows (EPM is defined analogously): SPM 2 σ σ = (7) where σ 2 is the statistial variane of the starting variants ourrenes, whih is alulated through the following formula: 1 2 B 1 N 2 2 σ = ( ) ( pi ) (8) N i= 0 N N is the number of variants addressed by the metri, while p i is the perentage of ourrenes for the i-th onfiguration variant. σ 2 B is instead the best ase variane, and is therefore alulated through eqn. (8), assuming that only one variant has been oherently used throughout the appliation. WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

10 472 ata Mining VI Table 2: SPM metri measurement sale. Metri s Range Measurement Sale Value 0 <= SPM<0.2 Insuffiient 0.2<= SPM<0.4 Weak 0.4<= SPM<0.6 isrete 0.6<= SPM<0.8 Good 0.8<= SPM<=1 Optimum The last step in the metris definition is the reation of a measurement sale, whih defines a mapping between the numerial results obtained through the alulus method with meaningful disrete values. The SPM metri adopts an ordinal nominal sale; eah nominal value in the sale expresses a onsisteny level, orresponding to a range of numerial values of the metris, as defined in table 2. The same sale overs EPM metri too. 6 onlusions In this paper, we proposed a methodology and provided metris for mining effetive design solutions at the WebML oneptual shema of an appliation. Moreover, we illustrated a quality evaluation tehnique for the solutions retrieved by means of onsisteny. This methodology when applied to a large number of WebML appliation shemas provides a mehanism for the identifiation of templates in speifi domain Web appliation frameworks and an form a valuable tool for hypertext arhitets for the identifiation of Web design patterns. We are urrently working on loating more preise metris for the seure extration of design solutions. Furthermore, applying the methodology to a large number of appliations, in order to fine-tune it, is one of our goals. Referenes [1] Retshitzegger, W. & Shwinger, W., Towards modeling of dataweb appliations - a requirements perspetive. In Pro. of MIS, vol. 1, [2] lexander,., Ishikawa, S., Silverstein, M., Jaobson, M., Fiksdahl-King, I. & ngel, S., Pattern Language, Oxford University Press, [3] Shwabe,, Esmeraldo, L., Rossi, G. & Lyardet, F., Engineering Web ppliations for Reuse. IEEE Multimedia, 8(1), pp.20-31, [4] eri S., Fraternali, P. & Matera, M., WebML ppliation Frameworks: a oneptual Tool for Enhaning esign Reuse. In Pro. of WWW10, [5] WebRatio, [6] eri, S., Fraternali, P., Bongio,., Brambilla, M., omai, S. & Matera, M., esigning ata-intensive Web ppliations, Morgan Kauffmann, WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)

11 ata Mining VI 473 [7] eri, S., Fraternali, P. & Matera, M., oneptual Modelling of ata- Intensive Web ppliations. IEEE Internet omputing, 6(4), pp.20-30, [8] Fraternali, P., Matera, M. & Maurino,., WQ: an XSL Framework for nalyzing the Quality of Web ppliations. Pro. of IWWOST'02, [9] GraphGrep, [10] Garey, M.R. & Johnson,. S., omputers and intratability: guide to NP-ompleteness, Freeman, [11] Yan, X. & Han, J., losegraph: Mining losed Frequent Graph Patterns. Proeedings of the 9th M SIGK03, pp , ugust [12] Lehner, S. & Shrefl, M., efining web shema transformers by example. In Proeedings of EX 03, Springer, WIT Transations on Information and ommuniation Tehnologies, Vol 35, 2005 WIT Press ISSN (on-line)