Adaptive Knowledge-Based Visualization for Accessing Educational Examples

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1 Adaptve Knowledge-Based Vsualzaton for Accessng Educatonal Examples Peter Bruslovsky, Jae-wook Ahn, Tbor Dumtru, Mchael Yudelson School of Informaton Scences, Unversty of Pttsburgh {peterb, jaa38, Abstract A number of research teams are workng to organze personalzed access to the modern repostores of educatonal resources. The goal of personalzed access s to help students locate resources that match ther ndvdual goals, nterests, and current knowledge. The project presented n ths paper s focused on the least explored way of personalzed access adaptve vsualzaton. Here, we present the NavEx ADVISE vsualzaton system, whch provdes personalzed access to a repostory of educatonal examples. The system combnes spatal, smlarty-based vsualzaton wth adaptve annotatons of resources. The spatal layout and the adaptve annotatons are generated usng a knowledge-based ndexng of examples wth doman concepts. 1. Introducton Dedcated repostores of educatonal materals such as educatonal dgtal lbrares (DL) and pools of reusable learnng objects are now accumulatng a large volume of educatonal resources. The abundance of resources avalable to students has created a new challenge how to help students locate resources that match ther ndvdual goals, nterests, and current knowledge. We frst faced ths challenge n our WebEx project, when we developed a repostory of about a hundred annotated program examples for an ntroductory programmng course [2]. The repostory contans lnes of example code that has been annotated by teachers. Once an example s selected, the WebEx system allows students to explore t nteractvely nsde a Web browser, by clckng on the annotated lnes of code and readng the teacher s explanatons. But the queston s how can the most relevant examples n a repostory be located when there are dozens of examples accessble at any one tme? Our frst soluton was to apply the adaptve navgaton support approach by usng NavEx [9], an adaptve nterface for the WebEx system. It provded a lst of lnks to all examples and augmented each lnk wth an adaptve con that vsualzed the status of the example, adapted to the current state of the student's knowledge and hstory of past nteractons (Fgure 1). These cons help students to: a) dstngush new examples from examples that have already been partally or fully explored n the past; as well as to b) dstngush examples that are ready to be explored from examples that demand prerequste knowledge the student lacks. The problem that we are addressng n ths paper s how to help students to locate examples that are relevant not only to ther current knowledge, but also to ther current learnng goal. What f a student has problems wth understandng a specfc example and wants to read explanatons for one or more smlar examples? Or, n contrast, what f a student fully understands the programmng constructs explaned n a specfc example and now wants to explore an essentally dfferent example to better cover the content of the course? Unfortunately, the ordered lst of lnks to examples used n NavEx offered no help n selectng smlar or dssmlar examples. Past research on nformaton vsualzaton suggests that goal-based selecton of documents s better supported by two-dmensonal vsualzaton than by a onedmensonal lst. In partcular, the Lghthouse system [5] appled spatal smlarty-based vsualzaton and relevance markng to assst users n fndng documents most relevant to ther search goals. Due to the nature of smlarty-based vsualzaton, smlar documents were postoned close to each other and dssmlar far from each other. Ths allowed the users to vsually receve better gudance n selectng documents than s usually provded by a ranked lst. Ths paper presents our attempt to mplement deas of adaptve vsualzaton n the context of personalzed access to a repostory of annotated program examples. We present our new vsualzaton nterface, NavEx ADVISE, whch combnes spatal smlarty-based vsualzaton wth adaptve annotatons. The smlarty-based layout allows students to easly locate the most smlar and dssmlar examples vsually, helpng the student to select examples relevant to ther current learnng goal. Adaptve annotatons support knowledge-based and progress-based adaptaton. NavEx ADVISE was mplemented usng ADVISE 2D, a vsualzaton tool developed by the authors.

Fgure 1 Adaptve navgaton support n NavEx system helps students choose the example to browse by augmentng each example lnk wth an adaptve con that vsualzes the status of the example The need to provde

2 Fgure 1 Adaptve navgaton support n NavEx system helps students choose the example to browse by augmentng each example lnk wth an adaptve con that vsualzes the status of the example The need to provde personalzed access to program examples served as the motvaton to develop ADVISE 2D; however, we attempted to make ADVISE 2D generc enough so that t can support a range of smlar nformaton access needs. The paper focuses on both NavEx ADVISE, a specfc adaptve vsualzaton system, and ADVISE 2D, a tool that we have created to support ths and smlar projects. The next secton presents the user's vew of the adaptve vsualzaton nterface n NavEx ADVISE. The remanng sectons present ADVISE 2D and ts applcaton to gudng students through examples wth personalzed access. 2. Accessng program examples wth adaptve vsualzaton The vsualzaton-based nterface for accessng examples organzes and dsplays the whole repostory of examples on a two dmensonal example map. Fgure 2 shows the map wth ts examples dstrbuted accordng to smlarty. Each rectangle represents an example. The dstance between two documents on the map represents how smlar they are to each other. If ther knowledge-level content s smlar, they are placed closer to each other, but f dssmlar, they are placed farther from each other. It s mportant to know that the vsualzaton s based on knowledge-based smlarty. The dstance between two examples s determned by comparng the set of programmng concepts presented by these examples. Each example bears an adaptve con that shows the relevance of ths example to the user's current knowledge and completon of progress through the example. If the user s not ready to access the example, due to a lack of prerequste knowledge, a red X s dsplayed (Fgure 2). If the user s ready to access an example, then a green bullet s shown. The fullness of the bullet approxmates the user's progress wthn the example. An empty bullet shows a completely new, but ready-to-be explored example. A flled bullet denotes a fully explored example. The current con s determned by the NavEx system, whch compares the past hstory of the student's nteracton wth the example to the concept-level model of knowledge mantaned by NavEx. The spatal layout and adaptve annotatons help the users to locate the most relevant examples. To start workng wth an example, the user double-clcks the example box, whch causes a WebEx wndow to open for nteractve exploraton of the selected example. To better explore the set of examples, users can manpulate the vsualzaton: zoomng n or out wth a slde bar or pannng the screen n four drectons. In addton, users can dsplay lnes between smlar documents and exact smlarty values between pars of documents.

Fgure 2 ADVISE 2D helps students choose the most relevant example by combnng adaptve navgaton support wth spatal 2D vsualzaton of the example space These functonaltes are mportant for dealng wth an

3 Fgure 2 ADVISE 2D helps students choose the most relevant example by combnng adaptve navgaton support wth spatal 2D vsualzaton of the example space These functonaltes are mportant for dealng wth an abundance of documents that may potentally be dsplayed n a relatvely small wndow. Fnally, the example names sometmes make the dsplay too crowded to grasp the whole pcture. In such stuaton, the rectangles wth document ttles can be reduced to small cons, as shown n Fgure 3. In ths vew, the example name s only dsplayed when a user moves a mouse cursor over ts con. 3. Smlarty-based vsualzaton n ADVISE The spatal vsualzaton of examples n NavEx was produced wth ADVISE 2D one of the tools developed n our lab for the ADVISE project. ADVISE (ADaptve VISualzaton for Educaton) s a sute of web-based, personalzed document-vsualzaton systems for educatonal purposes. The goal of the ADVISE project s to help students fnd the most relevant educatonal materals, through personalzed vsualzaton. ADVISE sute ncludes three systems wth dfferent perspectves and approaches. ADVISE 2D and ADVISE 3D are smlarty-based document space vsualzaton systems for two- and threedmensonal spaces, respectvely. They provde spatal document maps where documents are dstrbuted accordng to ther smlarty values. (We refer to every educatonal object n ths system as a document.) ADVISE VIBE s an mplementaton of the VIBE [7] document vsualzaton approach. It calculates smlartes between documents and POIs (Pont Of Interest) or concepts and determnes document postons relatve to the postons of the POIs. ADVISE tools are customzable to dfferent applcaton contexts and are avalable from the project home page ( ADVISE 2D s a generc tool that provdes personalzed access to documents usng a smlarty-based vsualzaton approach known as sprng modelng (see secton 3.4 for detals). Icons whch represent smlar documents are postoned relatvely closer to each other on a two dmensonal map and whle those whch are dfferent would be placed more dstantly on the map. By consultng the dstrbuton of the cons and the postons of each of them, users can make some general assumptons about the contents of a document even before actually openng t, understand the relatonshps between documents n terms of ther contents, and see the overall pcture of the documents n the corpus. The adaptve smlarty-based vsualzaton s produced n several steps: representng document contents as vectors, loadng the vectors nto the applcaton, calculatng smlartes among document vectors, decdng document postons on a two dmensonal space based on these smlarty values, and fnally presentng vsual representaton to users.

4 scheme can be appled for term weghts. TF means the frequency of a term n a document and IDF s an nverse of the number of documents whch have the correspondng term (Equaton 1). Fgure 3 Smple dsplay for documents Term 1 Term 2 Term 3 Term Doc 1 w 11 w 12 w 13 w 1j Doc 2 w 21 w 22 w 23 w 2j Doc w 1 w 2 w 3 w j Fgure 5 Document-term matrx D tfdf ( d, t) = tf ( d, t) log df ( t) tf(d,t): number of occurrences of term t n document d df(t): number of documents where term t appears D : total number of documents n the corpus Equaton 1 TF-IDF weghtng Fgure 4 ADVISE 2D archtecture ADVISE 2D was desgned as a context-ndependent Web-based vsualzaton tool. It can vsualze data that has been loaded from several dfferent applcatons. Fgure 4 s the archtecture of ADVISE 2D. For the purpose of ths project, ADVISE 2D was tuned to work wth a repostory of WebEx examples. The remanng part of ths secton descrbes ADVISE 2D and the next secton presents use of the system for personalzed access to examples Document representaton Documents n ADVISE 2D are represented as weghted term vectors n order to calculate the smlartes and to place them n approprate postons [8]. If a document s a full-text tutoral or a lecture slde, terms from the document are extracted and stored n a vector, whch represents the document. If the document s a code example, language constructs are stored n the vector. Therefore, the whole corpus can be represented as a matrx wth documents n ts rows and terms n ts columns. If the corpus contans a total of M documents and the total number of terms n t s N, an M by N matrx s constructed (Fgure 5). In most cases, few documents would even come close to contanng every term n the corpus, so the matrx tends to be very sparse, wth a lot of 0 s, whch means that there s no occurrence of another correspondng term n the document. The value of vector components can be bnary or weghted. A well known TF (term frequency) or TF-IDF (term frequency multpled by nverse document frequency) 3.2. Smlarty calculaton The cosne smlarty coeffcent (Equaton 2) was used for calculatng nter-document smlartes. Ths relates to the cosne angle of the two vectors x and y, and ranges from 0 (the two documents beng completely dssmlar) to 1 (they are dentcal). Sm( x, y) = x 2 x y Equaton 2 Cosne smlarty coeffcent 3.3. Data communcaton ADVISE 2D was desgned to work seamlessly wth webbased materals. It can spatally map the materals by ther contents, explore the mappng, and open ther contents by connectng to ther URL s. For ths last purpose, t was mplemented as a Java applet and can launch wthn web browsers. It loads three types of data to make the vsualzaton: a) document vectors wth ttles, b) lst of terms, and c) document URL s. They are fed nto the applet n two dfferent ways: usng <PARAM> tags n HTML- and XMLbased communcaton wth a server. The frst method works n a statc manner, whch cannot dynamcally update the contents beng vsualzed but the second method makes t y 2

5 possble for the applet to send a request to the server for new data, enablng the applet to update the current vsualzaton. The applet and the server communcate n a predefned XML-formatted protocol Spatal mappng wth the sprng model ADVISE 2D organzes and vsualzes documents based on the sprng modelng algorthm. The sprng modelng algorthm or FDP (Force Drected Placement) s a heurstc approach to graph drawng, based on a hypothetcal physcal (mechancal) system n whch the graph s edges are replaced by sprngs whle the vertces (nodes) are replaced by rngs. The sprngs attract the rngs f they are too far apart and repel them f they are too close [1; 4]. It can be used to sort randomly placed nodes nto a desrable layout that satsfes the aesthetcs of vsual presentaton. F F s r = C s = C r log( d / C / d Equaton 3 The forces formula for the sprng model The forces actng on every node nclude sprng force and repulson force. The resultant of these forces can be calculated and, under the nfluence of sprng force between connected nodes and repulson force between unconnected nodes, the graph wll automatcally adjust tself untl the system reaches a stable state. It calculates ths resultant of forces by ncludng the sprng and repulson forces that act on every node, n an teraton of the loop untl the graph reaches a stable state [6]. Equaton 3 shows the calculatons of sprng force and repulson force n ths sprng model. Cs, Cd, Cr are constants such as sprng length, sprng stffness, sprng type, and ntal confguraton, whch control the forces actng on nodes and ther movements. In ADVISE 2D, both sprng forces and repulson forces were consdered to show ther relatonshps n terms of smlartes. When a system launches and reads n the data needed, t randomly places every document on the map. The sprng algorthm begns from ths state and terates untl t reaches a stable state. In ths stable state, the documents are arranged accordng to ther smlarty values and are then fnally vsualzed on the map. 2 d ) representaton of program examples produced by the NaxEx system [9]. As we mentoned n the ntroducton, NavEx was desgned to provde personalzed access to code examples through adaptve navgaton support. NavEx provdes gudance regardng relevant examples that students should or shouldn t explore by dsplayng an adaptve con (Fgure 7). To generate ths con dynamcally for each example, NavEx takes nto account the programmng knowledge presented by each example, the current state of the student's knowledge, and hs/her past nteracton wth the examples. 4.1 Knowledge-based example ndexng The key to ths functonalty s the knowledge-based ndexng of each annotated example wth a set of concepts from the C-programmng doman. The concepts used are C language constructs such as decl_var, vod, nclude, man_func, etc. The ndexng s done automatcally by a doman-specfc parser. After all examples are ndexed, concepts of each of the examples are splt nto prerequstes and outcomes. Outcomes are concepts that are llustrated by that example. Prerequstes are concepts that should be learned before explorng the example. The splttng s automatc, but t s drven by the teacher s ndvdual approach to concept- sequencng wthn the course. To tune the ndexng to a specfc teachng approach, a teacher must provde a set of representatve examples for each course lecture. More detals about the ndexng procedure can be found n [3]. The result of concept ndexng and dvson s shown n Fgure 6. Ths knowledge-based example ndexng was used by NavEx ADVISE to produce a spatal layout for the repostory of examples. The concept ndex of each example was converted nto a term vector as explaned n secton 3.1. To produce a course-ndependent layout, the ndexng does not dstngush prerequste and outcome concepts, but takes nto account how frequently each concept s found n each example (and some concepts can present n several places wthn the same example). The resultng layout s based on deep knowledge-level smlarty between the examples. 4. Customzng ADVISE 2D to work wth program examples To acheve the goals of our current project, our contextndependent system ADVISE 2D was customzed to provde adaptve knowledge-based vsualzatons of annotated program examples. The customzed system s referred to as NavEx ADVISE snce both the spatal representaton and the adaptve cons are generated usng the knowledge-based Fgure 6 Concept ndexng and dvson

6 4.2 The adaptve annotaton of examples The adaptve annotaton of examples n NavEx ADVISE was produced usng the same cons and algorthms as n the orgnal NavEx system. Thus the same example n the NavEx lst and on the NavEx ADVISE map bears an dentcal annotaton at the same moment n tme. Both vews provde two knds of annotaton: progress-based and prerequste-based. The progress-based annotaton shown as a partally-flled green bullet (Fgure 7) s calculated as smply the percentage of example code lnes already explored by the student, compared to the total number of annotated lnes n ths example. Computaton of prerequste-based readness for an example s based on a concept-level model of student knowledge. The example s consdered ready for exploraton f all of ts prerequste concepts are already known to the student to a specfed extent. The system approxmates the student's level of knowledge for each concept by montorng student actvtes wthn the system (.e., example exploraton) and by consultng a centralzed student model that collects evdences of student knowledge from multple sources (.e., readng a tutoral secton or answerng a quz). Not ready to be accessed Ready to be accessed Fgure 7 Annotaton clues n NavEx The adaptve annotatons support a natural flow for exploraton of concepts and examples. Once a student starts to work wth examples, only those that are ready to be accessed wll have no prerequstes. As a user explores an example and revews a certan number of annotatons (defned by a dynamc threshold), an example s consdered to be completed (although ther progress may reman below 100%). At the same tme, all of the assocated concepts are marked as learned. If there exst some examples whose prerequstes are now all marked learned, these open up to be explored and the flow contnues on. For more detals refer to [3]. Conclusons Ths paper presents our attempts to apply adaptve, knowledge-based vsualzaton to gude students of ntroductory programmng courses to most of the tems n a repostory of educatonal examples. We presented the NavEx ADVISE vsualzaton system, whch combnes a spatal smlarty-based vsualzaton wth the adaptve annotaton of educatonal objects. Both the spatal layout and the adaptve annotatons are generated by usng a knowledge-based ndexng of program examples wth programmng concepts. The system was developed by the targeted customzaton of the generc ADVISE 2D vsualzaton tool, whch had prevously been developed n our lab. Both the NavEx and NavEx ADVISE systems are currently beng used n an ntroductory programmng course. Our earler exploraton of NavEx demonstrated that students apprecate the gudance provded by adaptve annotatons and that t encourages students to explore sgnfcantly more examples [9]. Our current challenge s to determne the value of adaptve vsualzaton n ts role of supportng student access to educatonal examples. Acknowledgements Ths materal s based upon work supported by the Natonal Scence Foundaton under Grant No References [1] Battsta, G. D., Eades, P., Tamassa, R., and Tolls, I. G., "Algorthms for drawng graphs: an annotated bblography", Computatonal Geometry: Theory and Applcatons 4, 1994, pp [2] Bruslovsky, P., WebEx: "Learnng from examples n a programmng course", In: Fowler, W. and Hasebrook, J. (eds.) Proc. of WebNet'2001, World Conference of the WWW and Internet, Orlando, FL, AACE, 2001, pp [3] Bruslovsky, P., Yudelson, M., and Sosnovsky, S., "An adaptve E-learnng servce for accessng Interactve examples", In: Nall, J. and Robson, R. (eds.) Proc. of World Conference on E-Learnng, E-Learn 2004, Washngton, DC, USA, AACE, 2004, pp [4] Eades, P., "A Heurstc for Graph Drawng". Congressus Numerantum 42, 1984, pp [5] Leusk, A. and Allan, J., "Interactve nformaton retreval usng clusterng and spatal proxmty", User Modelng and User Adapted Interacton 14, 2-3, 2004, pp [6] Lu, X., Shzuk, B., and Tanaka, J., "Dynamc Parameter Sprng Modelng Algorthm for Graph Drawng", In: Proc. of Internatonal Symposum on Future Software Technology (ISFST2001), Zheng Zhou, Chna, 2001, pp [7] Olsen, K. A., Korfhage, R. R., Sochats, K. M., Sprng, M. B., and Wllams, J. G., "Vsualsaton of a document collecton: The VIBE system", Informaton Processng and Management 29, 1, 1993, pp [8] Salton, G., Automatc Text Processng, Addson-Wesley Publshng Co., Readng, MA. [9] Yudelson, M. and Bruslovsky, P., "NavEx: Provdng Navgaton Support for Adaptve Browsng of Annotated Code Examples", In: Loo, C.-K., McCalla, G., Bredeweg, B. and Breuker, J. (eds.) Artfcal Intellgence n Educaton: Supportng Learnng through Intellgent and Socally Informed Technology. IOS Press, Amsterdam, 2005, pp

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