The most recent OHS, Auld Linky [Michaelides et al., 2001], developed at the University .... Figure 1. Taxonomy of adaptive hypermedia technologies [Brusilovsky, 2001] ..... This research is funded in part by EPSRC IRC project âEQUATORâ .... Conference on Hypertext and Hypermedia, (pages 37-38), August, 2001, Arhus,.
Adaptive Hypermedia through Contextual Structures CHRISTOPHER BAILEY, WENDY HALL, DAVID E. MILLARD, MARK J. WEAL ________________________________________________________________________ Research at the University of Southampton has extended generalised Open Hypermedia (OH) models to include concepts of context and behaviour, both traditionally very important to the Adaptive Hypermedia (AH) domain. In this paper we re-evaluate Brusilovsky’s taxonomy of AH techniques from a structural perspective. The authors show that it is possible to identify and model common structures across the taxonomy. An agent based adaptive hypermedia system called HA3L is presented, which uses OH structures to provide a straightforward implementation of a variety of adaptive hypermedia techniques. This enables us to gain a new perspective on the relationship between the techniques and informs the design of future adaptive hypermedia systems. Categories and Subject Descriptors: Adaptive Hypermedia, Open Hypermedia General Terms: Additional Key Words and Phrases: Adaptive Techniques, Hypermedia Structure, FOHM, taxonomy
________________________________________________________________________ 1. INTRODUCTION Open Hypermedia (OH) and Adaptive Hypermedia (AH) have developed as two major strands of hypermedia research. Open hypermedia research has focused on issues such as interoperability [Davis et al., 1997; Davis et al., 1999; Reich et al., 1999] and reference models [Furuta & Stotts, 1990; Halasz & Schwartz, 1994; Hardman, 1994]. Adaptive hypermedia, having grown out of fields such as artificial intelligence, intelligent tutoring systems and user modeling [Sleeman & Brown, 1982; Böcker et al., 1990], has focused more on what information should be presented to users and how it should be adapted to their needs [Brusilovsky, 1996]. Brusilovsky defines adaptive hypermedia systems as those that “build a model of the goals, preferences and knowledge of each individual user, and use this model throughout the interaction with the user, in order to adapt to the needs of that user.” [Brusilovsky, 2001] The purpose of this paper is to produce an alternative view of the AH domain from a contextually aware OH perspective. To this end we will be using Brusilovsky’s taxonomy of adaptive techniques [Brusilovsky, 2001]. We will show that many of the techniques in the taxonomy can be implemented with a small key group of hypermedia structures. This structural perspective is used to analyse and critique the taxonomy and inform the continued development of our contextual link server.
In this paper we will first look at the background of OH and AH and set out the motivations for the work that we have carried out. Brusilovsky’s taxonomy of adaptive hypermedia techniques will then be presented, followed by a breakdown of the taxonomy focusing on the underlying hypermedia structures that are needed to implement the techniques contained in the taxonomy. A number of points arising from this structural overview are discussed before a novel system HA3L is described, illustrating how our structural approach can be coupled with an agent-based architecture to implement many of the techniques described in the taxonomy. Finally, issues arising in the implementation of certain techniques are discussed and conclusions drawn as to the possible benefits of a structural approach to adaptive hypermedia and the implications for the underlying contextual structure servers. 2. BACKGROUND In the late 1980’s, the hypermedia research community developed, amongst others, two separate research threads; one focusing on Open Hypermedia systems and one on Adaptive Hypermedia systems. The AH community arose partly from the extensive work that had already been conducted into artificial intelligence and partly from Intelligent Tutoring Systems (ITS). AH researchers are primarily concerned with using pre-existing methods and techniques found in the fields of AI, ITS and user modeling, and extending, combining and merging these ideas to create complete systems that understand and aid the user in knowledge acquisition. ITS promoted the development of educational server-side adaptive web-based systems such as MANIC [Stern & Woolf, 1998], INTERBOOK [Brusilovsky et al. 1998] and more recently AHA! [De Bra & Calvi, 1998][Brusilovsky et al., 2003]. Other such server-side systems index web sites [Perkowitz & Etzioni, 1999] or provide personalized interfaces to large hypermedia systems [Espinoza & Höök, 1997]. AH has also seen the development of client-side adaptive systems that follow users as they browse the World Wide Web. Examples of these systems include WebMate [Chen & Sycara, 1998], Letizia [Lieberman, 1995] and LiveInfo [Maglio & Farrell, 2000]. The second thread of hypermedia research focused on the Open Hypermedia field. Open Hypermedia Systems (OHSs) such as Microcosm [Fountain et al., 1990], Chimera [Anderson et al., 1994] and DHM [Grønbæk & Trigg, 1994], separate links from
documents, allowing hyperstructure to be processed separately from the media it relates to. In recent years the OH community has tackled the issue of interoperability between different OHSs, in particular the development of the Open Hypermedia Protocol (OHP) [Davis et al., 1996]. The scope of the OHP project evolved into an attempt to create a reference model and architecture for OHS in general. This change focused the OH community on the fundamental structures that such systems deal with, which has resulted in the promotion of structure to a first-class status and the consideration of how context might affect that structure. In particular the development of the Fundamental Open Hypermedia Model (FOHM) [Millard et al. 2000; Millard, 2000] deals directly with issues of context, and behaviour that can modify context. The most recent OHS, Auld Linky [Michaelides et al., 2001], developed at the University of Southampton, is a contextual structure server that maintains and provides structures expressed in FOHM. It has been used as a general contextual structure server to support a wide variety of hypermedia systems ranging from an Augmented Reality interaction system [Sinclair et al., 2002], to work on hypertext short fiction based on sculptural hypertext [Weal et al., 2001b]. Auld Linky is the latest in a long line of link services that have arisen from research at Southampton which have been progressing steadily towards the integration of agent-based computing, structural OH systems and AH. 3. MOTIVATION In this section we will look at the history of AH research in Southampton’s IAM group which has led to the development of the models and systems presented in this paper. The Open Hypermedia system Microcosm, first designed in 1989, could be viewed as a framework for Adaptive Hypermedia systems, although this term had not been coined at the time. Microcosm is considered to support adaptation for two main reasons. Firstly, being one of the original Open Hypermedia Systems, the links were stored in linkbases and any subset of the available linkbases could be applied at any time, either when the user logged into the system, or dynamically as the users interacted with the system. So it was relatively easy in Microcosm to develop hypermedia applications that were configured for different users depending on which linkbases were applied. Secondly, the Microcosm architecture was based on the use of chained filters which processed
messages created when the user interacted with Microcosm through a viewer or a thirdparty application set up to communicate with Microcosm [Hall et al., 1996]. Linkbases were implemented as filters, but filters could also be programmed to create links dynamically or more generally to adapt or configure the material in the application. So the user model/profile required by the AH system could be implemented as a Microcosm filter. Filters have been used to implement what are considered traditional adaptive techniques, such as adaptive navigation support i.e. presenting links in different colours depending on the background knowledge of the user (e.g. green for ‘read this now’ and red for ‘too advanced’) [Weber & Möllenberg, 1994], for adaptive presentation such as shading material that the system believes the user does not need to read [Hothi & Hall, 1998], and for the production of adaptive maps based on the users current location [Wilkins, 1994]. The use of Microcosm to develop an adaptive hypermedia application was first reported in Hothi & Hall [1998]. This was an educational hypermedia application in the area of archaeology. In the first experiment, Hothi & Hall used a simple static user model and applied different linkbases for different types of users before they worked with application. In the second experiment, a filter was used to generate a different (adapted) version of the hypermedia application according to the type of user as determined by the user model. More recently at Southampton we have been applying software agent technology to AH systems research. In our work on distributed information management, the Microcosm hypermedia system has evolved into an agent framework for distributed information management (the Microcosm filters have become agents) and several different Webbased link services [Moreau et al., 2000]. Agents present a modularized approach to programming which is well suited to the development of hypermedia systems. While the hypermedia community has largely ignored agents, they offer many features that are applicable to dynamic and adaptive situations. This has been reflected in the many recommender systems which have been built with agents such as FAB [Balabanovic & Shoham, 1997], QuIC [El-Beltagy et al., 2001] and Personal WebWatcher [Mladenic, 1996].
Ongoing research has led to the Southampton Framework for Agent Research (SoFAR), which provides developers with a Java based framework for developing social, autonomous, proactive and reactive agents [Moreau et al., 2000]. An example of its application is the Dynamic CV system, which used OH techniques as an interface to an underlying agent-based ontological information system [Weal et al., 2001a]. This provides the underpinning framework for the system described in Section 7. We have also developed a simple AH system within this framework where one agent maintains the user profiles, another agent controls access to the links provided by an external link server (called the Distributed Link Service (DLS) [Carr et al., 1995]), and a third agent acts as the user interface agent by matching the user profile, for the particular user, with the links appropriate for that user profile from the DLS linkbases [Bailey & Hall, 2000]. Those links are then presented to the user in the context of the application material they are looking at via a proxy server. Other work at Southampton has used Auld Linky to look at the way context can be used to modify structure; these include the Equator City project that has looked at hypermedia in physical spaces [MacColl et al., 2002], work on hypertext short fiction based on sculptural hypertext [Weal et al., 2001b] and the ArtEquAKT project which produces tailored biographies of artists from knowledge extracted from the web [Alani et al., 2003]. The systems developed for the work above have explored some of techniques within adaptive hypermedia; specifically adaptive link presentation, text fragment modification based on user preferences and addressed issues of modality of presentation. This work has led us to the observation that many of the current AH techniques can be described and supported with a simple set of contextual structures. 4. A TAXONOMY OF ADAPTIVE HYPERMEDIA Fig. 1 shows Brusilovsky’s taxonomy [Brusilovsky, 2001], which was itself updated from Brusilovsky [1996]. This diagram will be used as a basis for a structural comparison of OH and AH techniques.
The taxonomy focuses on user perception of the adaptation and interaction, and has been divided into two distinct areas: ‘Adaptive presentation’ and ‘Adaptive navigation support’. Adaptive navigation support focuses on aspects of navigational hyperlinks such as generation, appearance, spatial placement and functionality. Adaptive presentation systems rely on information chunks (or fragments) that can be processed and rendered in a variety of ways depending on the user preferences. In broad terms, adaptive navigation support is about links while adaptive presentation about content.
Adaptive Multimedia Presentation Adaptive Presentation
Adaptive text presentation Adaptation of modality
Adaptive Hypermedia Technologies
Natural Language adaptation
Inserting/removing fragments Altering fragments
Canned text adaptation
Stretchtext Sorting fragments
Direct guidance Dimming fragments
Adaptive navigation support
Adaptive link sorting
Hiding
Adaptive link hiding
Disabling
Adaptive link annotation
Removal
Adaptive link generation Map adaptation
Figure 1. Taxonomy of adaptive hypermedia technologies [Brusilovsky, 2001]
While the distinctions of the taxonomy are important for identification and classification of adaptive hypermedia systems, the implementation of these techniques can be achieved using a small selection of fundamental data structures that can be combined to create powerful AH systems. The next section presents an analysis of the taxonomy in terms of the contextual open hypermedia structures that might be used to implement the techniques. It is our intention that these structures will provide an abstraction between the front end interface and the underlying adaptation techniques.
5. A STRUCTURAL APPROACH TO THE TAXONOMY The Fundamental Open Hypermedia Model (FOHM) [Millard et al., 2000; Millard, 2000] provides a model for representing hypermedia structures and in addition has a clearly defined notion of context, and how that context affects views of the structure. In FOHM, a context object is a collection of meta-data with an associated matching function; the basic example being a set of attribute-value pairs. Context objects can be attached to various parts of the hyperstructure and describe which contexts that part can be seen in. FOHM also contains behaviour objects. These can be attached to the structure informing clients to take an action given an event, for example, updating the user model when a document fragment is viewed. When coupled with context these two mechanisms enable the techniques of adaptive hypermedia to be expressed more formally using different types of contextual structure. In the semantic web [Berners-Lee et al., 2001], objects and relations are modeled as RDF-Triples. RDF does not contain the higher-order structures required to support the taxonomy, however the semantics for these can be defined using RDF Schema. We have chosen to use FOHM here, as it does support these structures natively using typed, n-ary relationships. A fuller discussion of the relationship between RDF and FOHM can be found in Gibbins et al. [2003]. FOHM provides an underlying data model that is implemented in the Auld Linky contextual structure server. Auld Linky functions as a link service in that it stores links and answers queries on the link structure. It provides pattern matching services over HTTP, both the query patterns and link structures are expressed using XML. When a client sends a query to Auld Linky a context object can be included. If the query context fails to match the structure context then that part of the structure is removed. Auld Linky then collapses the remaining structure to retain integrity before returning it to the client. We call this the context culling process. In this way clients receive a contextual view of the structure. In the next sections we look at the various FOHM structures that might be used to implement the techniques described in Brusilovsky’s taxonomy.
5.1 Data Object The most basic object in FOHM is the data object. This is a wrapper for any resource that lies outside of the hyper-structure (for example, the url of a file or stream). It may also contain a fragment of content, such as a paragraph of text. Data objects may have context objects attached to them that describe which contexts the data object is visible in. They may also have behaviour objects attached to them that describe actions that clients should take given certain events (for example, to update the client’s user model when the file referred to by the data object is displayed). Figure 2 shows a diagram of a data object with a context and behaviour attached.
Data Context
text
Behaviour Figure 2. A Data Object in FOHM
Dimming Fragments The simple metadata inside the context object can be used by an application to help it decide how different data fragments should be presented; for example, using metadata from the context object in order to judge whether the fragment should be displayed normally or dimmed. 5.2 Navigational Link A fundamental element of structure in FOHM is an association. This is a collection of references, each bound to the association via a binding object that describes why it is a member. The association has a structure type and basic metadata (such as a description). References are elements that either point into or at data objects or other associations. Context and behaviour can also be attached to all of these objects. Associations can be used to model OHS typed n-ary links. In this case the association is of type ‘Link’ and each binding must specify whether the attached reference is a source, destination or bidirectional member. Figure 3 shows a navigational link expressed in FOHM. The context object expresses which context this association is visible in, while the behaviour defines any actions for a client, for example, to update the user model if this link is traversed.
Association
Link SRC
BI
DEST
text
text
Binding Reference
text
Figure 3. A Link in FOHM
Adaptive Link Hiding Similar to the dimming fragments technique, the metadata inside the context objects can be used by the system to decide how to present links to the user. Of Brusilovsky’s three sub-techniques, hiding and disabling [De Bra & Calvi, 1998] can be done by a client after reading the metadata in the context object, while removal [Brusilovsky & Pesin, 1998] can be done by the server during the context culling process. 5.3 Concept Another type of association that we have found useful is the concept. This is a set of references that each portray a different view or perspective on the same conceptual entity. These might differ semantically (for example, different descriptions of a product for different markets) or syntactically (for example, the same description in different languages). Figure 4 shows a concept. Here, the context objects are attached to the data objects at the leaves of the structure. Context objects are not always attached to the top level structure. In the case of the concept, the context objects could be attached to the binding, the reference, or on the referenced data objects in the structure, (for example, while a client might be able to see that a data object exists in a particular context they might not be able to see that it is a member of a concept structure).
Two of Brusilovsky’s techniques may be implemented with the concept structure and they map roughly to the syntactic and semantic notions of conceptuality that we have described above.
Concept
text
image
audio
Figure 4. A Concept in FOHM
Adaptation of Modality Choosing between different representations of the same data [Specht & Oppermann, 1998] is a form of syntactic concept. In this case the various formats that represent the same information are grouped together in one concept and the media type presented to the user is decided dynamically by both the context culling process (which will remove inappropriate formats) and the client, which may now decide between the remaining formats illustrated in Figure 4. Altering Fragments Choosing between alternative fragments of the same media [De Bra & Calvi, 1998] is a form of semantic concept. In this case the various ways of expressing the same idea are grouped together in a concept and chosen in exactly the same way as different modalities. These techniques can be used together to choose between alternative fragments that may have both different media formats and different semantic content. 5.4 Tour Members of an association can also be ordered. The tour structure is a simple example of this, where members of the association are meant to be viewed in a sequence. This might be a sequence of documents, in which case the tour is analogous to a series of binary
links, or it might be of media fragments. In this later case the tour is acting as a virtual composite document that must be rendered by a client before it can be presented to a reader as if it were a real document. Figure 5 shows a tour across a sequence of different media fragments.
Tour 1
2
3
4
5
text
text
image
audio
text
Figure 5. A Tour in FOHM
Inserting / Removing Fragments Inserting or removing fragments of a document to tailor the content to a particular reader [Hohl et al., 1996] can be achieved easily with a contextual structure if the document in question is encoded as a virtual document using a tour structure. Each fragment in the tour has a context object that describes in which context that fragment becomes a member of the tour and thus in which contexts it appears in the document. When the client retrieves the tour in a particular context the inappropriate members are culled away. The client can then render the remaining members of the tour and dynamically create a tailored document. 5.5 Level Of Detail A very similar structure to the tour is the Level of Detail (LoD) structure. This is also an ordered list of objects, however the semantics of the structure are more akin to a concept. In a LoD the members all represent the same conceptual entity which is described in an ascending level of detail. So the fragment at a higher position in the LoD will have more detail than one at a lower position. Figure 6 shows a LoD that contains four text documents, each of which concerns the same conceptual subject and each of which is more detailed than the one in the previous position.
LoD 1
2
3
4
text
text text
text text text
text text text text
Figure 6. A Level of Detail structure in FOHM
Stretchtext A LoD structure can be used to represent the information behind the stretchtext technique, where text in a document can be expanded by the user to reveal more information [Espinoza & Höök, 1996]. The text is placed in the LoD structure so that text depth relates to position. Context objects attached to the fragments describe in which context this particular depth of text is appropriate. When the LoD is retrieved in context the structure server culls away any depths that are inappropriate in the context (for example, they are too shallow for the user’s current preferences or contain references to material that the user is unfamiliar with) and the client can then choose from the remaining ordered fragments (i.e. could choose the shallowest remaining fragment for brevity, or the deepest remaining fragment for detail). 5.6 System Information In any adaptive system, it is inevitable that sources of adaptation arise from information outside the domain models. This is most obvious in collaborative recommender systems where the decision of which information to recommend is based on the experiences of other users of the system. Information of a dynamic nature is not ideally suited to being stored within FOHM due to the structured nature of the format. Instead this information might be better kept in more appropriate formats such as access logs, user models or implicitly within the system itself. We refer to this type of miscellaneous data as System Information. There are three techniques in the taxonomy that rely on this type of information.
Adaptive Link Generation The trails of documents visited by other users can be used to dynamically generate links. The trails can be used to infer relationships between frequently visited but unlinked information or to discover new resources and create links to them on the fly. Once created it would be possible to store these new links as FOHM navigational links, however the generation process itself has no reliance on FOHM objects. Debevc et al. [1997] demonstrates the use of link generation using system information. Map Adaptation Map adaptation describes the process of orientating a user within an information space, using a visual representation, Negro et al. [1998] provides an example of this technique. While the information used to provide map adaptation can originate from the current FOHM association, it is the user’s location (and their state) within the association that primarily resides in their user model. Adaptive Link Annotation Adaptive link annotation is a popular technique for adaptive systems whereby the appearance of a link reflects properties of the linked document as it relates to the user’s state. One popular technique often seen in adaptive systems is the traffic light metaphor developed in ELM-ART [Weber & Brusilovsky, 2001]. While it is possible to provide a variety of link styles grouped into a FOHM concept, clients still need to make a selection between styles based on some form of system information such as user preferences or goal. 5.7 Weight Metric The context culling process in Auld Linky is a simple binary decision. Either a structural branch matches and is included, or it fails to match and is culled. This black and white view of context is not always appropriate and several of the techniques outlined by Brusilovsky require a more fuzzy understanding of whether a structure is appropriate to view or not. What is needed in the contextual structure server is the ability to leave structural branches intact but with some form of weight metric that describes how appropriate they are in the context of the original query. Adaptive Link Sorting
Weight metrics can be used very simply to support adaptive link sorting [Hohl et al., 1996]. When the client queries for available links they do so in context. The resulting set of links includes some form of weight metric that describes how visible those links are in that context. This could be used by the client to order the links so that the ones that were contextually most appropriate appeared first or were emphasized in some way. Sorting Fragments The same effect could be achieved with data objects. This would be especially useful when combined with some of the previously discussed structures. For example, it could be used to help choose between the remaining members of a concept structure. 5.8 Multiple Methods Because the structures described here are quite generic sometimes they can be combined in different ways to achieve the same technique. For example, direct guidance (the principle of giving users a single adaptive ‘next’ option [Brusilovsky et al., 1998]) can be achieved in two ways: Direct Guidance as a Tour A tour structure could be used to rigidly arrange documents into a sequence. Each selection of ‘next’ would move the user along the tour structure. This is appropriate when static, authored paths are required through the material. Direct Guidance via Metrics Alternatively, a loose collection of Link structures could be used. When the links are retrieved the one with the highest weight metric could be used to select the destination of the ‘next’ navigation. This is useful when a much more dynamic type of guidance is desired, which changes as the set of available links grows. 6. REVISITING THE TAXONOMY Having discussed the fundamental structures that can be used to provide adaptivity and seen how they can be used in a novel adaptive hypermedia system, Figure 7 illustrates how these structures could be applied to implement the various adaptive techniques described in Brusilovsky’s taxonomy.
The legend in Figure 7 contains the two fundamental objects (data and links) and the extended FOHM structures. In addition, some of the techniques in the taxonomy require extra resources such as system information (e.g. user access logs), or a weight metric that describes not only which parts of the structure match in a particular context but also how well they match.
Figure 7. A structural view of Brusilovsky’s taxonomy that shows how FOHM structures can be combined to implement a range of adaptive hypermedia techniques.
Each technique in the taxonomy is built up using the structures or resources required to implement that technique. For example, ‘Adaptation of modality’ would require multiple data fragments, each representing the same information but using different media types. Concept structures would then collect these fragments together and the adaptive system would choose, based on a comparison of context tags and user models, which media fragment to present to the user. Key Issues arising from the taxonomy In Figure 7 we have highlighted a number of issues (labelled a to e) which we feel are worthy of further discussion.
(a) The only visual change to the taxonomy from Brusilovsky’s 2001 original, involves duplicating ‘Direct Guidance’ to reflect the two possible implementations we have previously discussed in section 5.8. (b) One of the philosophies behind OHSs is that there is a general view of data that covers all media types. From this perspective, it can be seen that any of the ‘Adaptive text presentation’ techniques described in the taxonomy can also be applied equally well to ‘Adaptive multimedia presentation’. To improve clarity, both techniques could be combined and re-labelled ‘Adaptive Media Presentation’. (c) This perspective also leads us to question the way that Natural Language (NL) adaptation is located as a sub-branch of text adaptation. Because we can envisage techniques equivalent to Natural Language processing for other media types, a better alternative would position NL adaptation under a larger umbrella of ‘Adaptive Sequencing’, which might use canned or constructed information fragments. Another issue with NL adaptation is how it influences nearly every single technique in the taxonomy. Whenever fragments of information are stitched together, the system may attempt to conserve the progression of the narrative flow. In these situations, sequencing methods like NL techniques can be used to smoothly merge fragments together. (d) Another consideration is that the various subcategories of ‘Adaptive link hiding’ (hiding, disabling and removal) are all structurally equivalent. This means that a system using navigational link objects to implement one adaptive link hiding method would have all the structures needed to implement any of the other adaptive link techniques. (e) The diagram also shows the apparent similarity between ‘Adaptation of modality’ and ‘Altering fragments’. These two techniques are functionally identical if one considers that fragments can contain multiple media representations of the same data objects. In such cases, choosing the best media type to display (adaptation of modality) is the same process as selecting one fragment from a set of fragments (altering fragments). Reflections on the Taxonomy Brusilovsky’s taxonomy originally provided a mechanism for classifying the various AH systems at the time. Since then, more systems have been developed, some of which fit in
to the existing taxonomy, and others that have forced extensions to the taxonomy making it more lengthy and complex. With our focus on structure we propose that many techniques described by the taxonomy as textual are in fact applicable to a wide range of media. It initially seems clear that the taxonomy divides structurally into two halves. The upper half is concerned with content, and requires a contextual data representation, while the lower half is concerned with navigation, and requires links with contextual membership. However, we have argued that direct guidance impacts on both halves of the taxonomy and therefore blurs the division of the taxonomy into presentation and navigation. In our opinion both adaptive presentation and adaptive navigation are about adaptive sequencing; the first is concerned with intra-document adaptive sequencing, the second in inter-document adaptive sequencing. The difference concerns the presentation of the sequence i.e. as a linearisation or as a hyperstructure. Other aspects of the taxonomy can also become blurred when viewed with a structural eye. In particular, map adaptation is concerned with the visualization of many other aspects of the taxonomy such as link hiding, altering fragments etc., rather than being a category in its own right. 7. IMPLEMENTATION To demonstrate the principles of using FOHM structures to support adaptive techniques, an agent-based adaptive hypermedia system was created to utilise each of the FOHM structures described in Section 5. The Auld Linky server was employed to provide these structures to implement a range of adaptive techniques, demonstrating the first use of Auld Linky in a traditional adaptive hypermedia environment. The system is called HA3L (Hypermedia Adaptation using Agents and Auld Linky). It dynamically generates web pages; adapting both the content and navigation of information across a single domain. The user is guided through the information space with a set of tours. The system comprises three agents, the user interface agent, the user model agent and the linky service agent.
7.1 Application Domain The data set used for this evaluation was taken from an existing adaptive web site called ‘JointZone’, which provides an educational adaptive hypermedia resource for medical students studying Rheumatology. Funded by the Arthritis Research Council, JointZone provides history-based link annotations for exploratory learning [Ng et al., 2002]. In addition to the 80 pages of text, there are images, video clips and Shockwave Flash demos to further explain specific concepts. The site also contains a glossary database of over 380 medical terms. JointZone stores all information in XML files, with each file representing a single web page concerning a specific topic. A page contains an optional summary paragraph, an introductory segment of text followed by a list of additional information. Pages are organized within a hierarchy of domain units such as rheumatic disorders, disease management and approach to patient. JointZone implements a range of adaptive techniques. For adaptive link hiding, the number of links presented to the user are manipulated according to the user’s knowledge level. Icons are placed next to links (link annotation) to indicate how much of a page a user has read. A ‘topic map’ provides a form of map adaptation whereby the system displays all the relevant documents associated with the current subject. JointZone also employs fragment altering by welcoming the user by name and showing them the status of their progress through the site. The JointZone XML pages of information were converted into the following FOHM structures: o
Navigational links, to represent each glossary item.
o
Data fragments, for each of the sections that make up a page. Context objects are attached to the fragments containing a ‘depth’ field to indicate the complexity of the data item. Summary fragments are labelled as ‘basic’, full introductions are labelled ‘extended’, while all additional information is labelled ‘detailed’. The glossary items and keywords for concepts that appear within the contents of the data fragment are expressed as Behavior objects, also attached to the data items.
o
Level of Detail structures, expressing the relationship between the summary, introductory and additional texts. There is one LoD structure for every page.
o
Concepts, used for situations where there is more then one media representation of the same data item.
A tour is created for each unit within the Rheumatology web site. The tour
o
follows the existing structure used in JointZone. Tours string together the LoD objects to form trails through the domain. They form the primary interaction mechanism for the web site. These structures allowed us to recreate the functionality of JointZone within HA3L and by exposing the implicit structure it becomes possible to implement other adaptive techniques using the same contextual mechanism. Figure 8 shows how the FOHM structures listed above can be combined to enable sophisticated adaptive effects to be achieved. This type of complex structuring is at the heart of our approach.
Tour: Approach to Patient 1
0
Tour: Introduction
Tour: Musculoskeletal Examination
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Level Of Detail: Overview
Principles of History Taking
The Hip
0 basic
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The spine
Video
The knee
The knee
Figure 8. FOHM structure of an oversimplified Rheumatology unit
7.2 Agents HA3L is built around a group of agents, written in the SoFAR agent framework. HA3L makes use of the Java based framework to develop autonomous, proactive and reactive agents. The simplified set of KQML performatives is used to communicate between the agents using a prescribed ontology.
Agents allow a modularised approach to programming which fits with the major components present in existing adaptive systems. HA3L requires user model, interface and adaptation services. Each service has been implemented as a single agent within the SoFAR framework, which allows each agent to dynamically discover, extend and invoke each other. The current implementation of HA3L comprises: o
A Linky service agent acting as a wrapper for the Auld Linky server allowing other agents to query and obtain FOHM structures. A FOHM ontology enables other agents to exchange FOHM structures and formulate queries to Auld Linky.
o
A User Model agent storing user preferences and recording the interactions with the system.
o
The Interface Agent providing the interaction mechanism between user and agent environment. It responds to HTTP GET requests converting the appropriate FOHM structures into HTML pages to send to the user. The interface agent uses the resources of the other two agents to apply various forms of adaptive content and navigation to the information.
7.3 System Design Using these three agents the system presents a set of tours through the domain. There are tours for each of the different units within the Rheumatology web site. After the user has selected a tour they can enter their preferences into the system, choosing between a ‘basic’, ‘extended’ or ‘detailed’ versions of the tour. These options correspond to the context variables associated with each data item in the FOHM server. The user can also choose their preferred media type, which corresponds to the use of concept structures within the domain that have multiple media representations. There is also an ‘automatic tour’ selection feature where the system chooses a tour based on the user’s past interaction history and most frequent preference selection. When the user has selected a tour, the Interface agent constructs the appropriate FOHM query and forwards it to the Linky agent which in turn queries the Auld Linky FOHM server. The response obtained by the Linky agent is returned to the Interface agent, which organizes the structures and constructs the appropriate web page. While the page is being
built, the Interface agent queries the User Model agent for specific information about which concepts and glossary items the user has seen before; this allows them to be rendered in a specific style depending on the user’s model. As the user travels through the tour, each new page on the trail is requested from the Interface agent who informs the User Model agent of the items the user has visited. Figure 9 shows an example page from a tour returned by the Interface agent.
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Figure 9. A screenshot of the adaptive system
7.4 Adaptive features As the user follows the tour or requests a glossary item, each user action is sent to the User Model agent for storage. The interface is divided into three panels. The main interface panel (labelled 1 in Figure 9) displays the current data fragment on the tour. Each page may contain text, images or video segments. Glossary items are rendered as hyperlinks within the text. When clicked, the glossary entry for that keyword appears in a popup window (shown in the screenshot). The Interface agent records this action and passes the information onto the User Model agent for storage.
If the user visits a new page that contained the same glossary item, the link is adaptively rendered in a different style. Because glossary items are implemented as FOHM links, all forms of adaptive link hiding (hiding, disabling or removal) are simply a matter of choosing a different presentation style. Currently, cascading style sheets are used to provide link hiding by rendering the visited glossary items in the same style as the main text. An example of link hiding can be seen in Figure 9, where the glossary item ‘collagen’, ringed on the screenshot, is coloured black (label 4). At the bottom of the page are buttons for navigating forward and backward though the current tour. These buttons move the user along the FOHM tour and therefore provide direct guidance. Additionally, if the user is viewing the first item of a LoD, then a ‘More Information’ button becomes active, allowing the user to iterate over each child node in the LoD. Iterating over the FOHM structures in this way mimics the ‘custom depth control’ approach taken by MetaLinks [Murray, 2002]. The system also provides a second form of direct guidance using automatic tour selection. Given the user’s preferences in selecting past tours, at the request of the user the Interface agent will query the user model and try and randomly select a new tour previously unseen by the user. If the user has seen every tour, the system will then pick one at random. The user preferences for the tour are chosen based on previous frequently chosen options. The choice of media preference, which is used to remove unmatched data fragments in FOHM concept objects, demonstrates adaptation of modality. The second panel in Figure 9, labelled (2), provides a form of map adaptation to the user by displaying a hierarchical overview of the tour. The current item shown in the main window is highlighted on the map. The user can jump to any data item by clicking on the relevant link on the map. In section 6 we described how system information is needed to provide map adaptation. In this system the information originates from the structures present in Auld Linky. The third information panel (3) presents the user with a list of concepts and glossary items associated with the current item displayed in the main window. Both of these elements use adaptive link annotation depending on the user’s history. Tick marks are placed next to the concept and glossary items the user has already seen.
This agent-based adaptive web site provides a range of adaptive features for a medical domain constructed using FOHM structures and maintained by Auld Linky. The attachment of context onto the FOHM structures allows adaptive rules to be incorporated into the structure of the domain. The inclusion of Behavior objects on data items provide a mechanism for updating the user model with visited concepts, which in turn are used to provide adaptive link annotation. Together they enable Auld Linky to act as an adaptation engine and provide a wide range of adaptive features that support the structural overlay taxonomy suggested in Figure 7. 8. CONCLUSIONS In this paper we have presented an agent based adaptive hypermedia system which takes some of the lessons learned from a structural open hypermedia approach and applies them to a traditional Adaptive Hypermedia system. We have used as our starting point Brusilovsky’s taxonomy of adaptive techniques, overlaying onto this a number of hypermedia structures, providing an alternative perspective on the taxonomy. This has two main aims; firstly as a means to inform AH research with the findings from the OH community, and secondly to see how the development of our contextual structure server Auld Linky, could be extended to facilitate established adaptive hypermedia techniques more easily. Our cross-domain viewpoint allows us to re-evaluate the taxonomy from a fresh perspective. In particular the focus on structure allows us to see that many techniques described by the taxonomy as textual are in fact applicable to a wide range of media. But what have we learnt about the capabilities of the Auld Linky contextual structure server? The breadth of structures supported by Auld Linky allow many, but not all, of the techniques detailed in the taxonomy to be implemented. Techniques requiring system information cannot be wholly implemented using Auld Linky. Although this system information could be modelled within the structures held in Auld Linky, often they are better held in a more natural location. For example user document trails may already be recorded in web logs and mirroring this information in Auld Linky may serve no practical purpose. Techniques requiring system information can be implemented using a combination of Auld Linky and a client with necessary external information sources such as web logs.
The two techniques that Auld Linky is currently unable to support are Adaptive Link Sorting and Sorting of Fragments. This is because Auld Linky lacks any form of weight metrics as part of its matching structure. The context culling works on Boolean matches. A structure either matches and is kept or doesn’t match and is deleted. This means there is no possibility of fuzzy matching; the collection of structures returned by Auld Linky is an unordered set with no matching metrics attached. For example we have an application where all links have a context value for complexity between 0 and 100. Auld Linky currently answers Boolean queries such as “give me all the links with a complexity greater then 50” but is unable to answer the query “give me the 10 most complex links in order”, in the latter case this implies an ordering based on the understanding that the higher the complexity the better the link. We are currently looking into adding metrics to Auld Linky, but this will necessitate overhauling the query mechanism to allow fuzzy queries and results. We also believe that any contextual OH server needs to provide for the problem domains being explored in AH research. To this end we are exploring the possibility of adding contextual weight metrics to the structures served by Auld Linky to allow it to support all the techniques described by Brusilovsky. As semantic web technology becomes more prevalent, previously implicit AH structures will need to be explicitly defined within a common framework (in this case ontological relationships). In this paper we have shown that by using OH formalisms these structures can be expressed in a semantically consistent manner. We believe that AH systems which recognise the structural equivalence of many AH techniques have an advantage as they will be able to handle adaptation consistently across different techniques and media. The application of an Open Hypermedia structural perspective to Adaptive Hypermedia techniques opens up new design approaches to the construction of Adaptive Hypermedia systems and shifts the focus from the presentation to the underlying structures being served. ACKNOWLEDGMENTS This research is funded in part by EPSRC IRC project “EQUATOR” GR/N15986/01.
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