Gjpm Geert-Jan Houben

Adaptive hypermedia: from systems to framework

The navigational freedom in conventional hypermedia applications leads to comprehension and orientation problems (Nielsen 1990). Adaptive hypermedia attempts to overcome these problems by adapting the presentation of information and the overall link structure, based on a user model. This paper introduces a framework for adaptive hypermedia systems (AHS). It briefly describes some popular methods and techniques for adaptation. Examples and evaluations of existing AHS are used to illustrate the potential benefits of using adaptation in hypermedia applications.

Hypermedia Presentation Adaptation on the Semantic Web

Web Information Systems (WIS) present up-to-date information on the Web based on data coming from heterogeneous sources. In previous work the Hera methodology was developed to support the design of a WIS. In this paper we target the design of an intelligent WIS. For this reason the Hera methodology is extended with two kinds of hypermedia presentation adaptation: adaptability based on a profile storing device capabilities and user preferences, and adaptivity based on a user model storing the user browsing history. While adaptability is considered to be static, i.e. the presentation is fixed before the browsing starts, adaptivity is dynamic, i.e. the presentation changes while the user is browsing it. The models used in Hera and their adaptation aspects are specified in RDF(S), a flexible Web metadata language designed to support the Semantic Web.

Hera: development of semantic web information systems

As a consequence of the success of the Web, methodologies for information system development need to consider systems that use the Web paradigm. These Web Information Systems (WIS) use Web technologies to retrieve information from the Web and to deliver information in a Web presentation to the users. Hera is a model-driven methodology supporting WIS design, focusing on the processes of integration, data retrieval, and presentation generation. Integration and data retrieval gather from Web sources the data that composes the result of a user query. Presentation generation produces theWeb or hypermedia presentation format for the query result, such that the presentation and specifically its navigation suits the users browser. We show how in Hera all these processes lead to data transformations based on RDF(S) models. Proving the value of RDF(S) for WIS design, we pave the way for the development of Semantic Web Information Systems.

XAL: an algebra for XML query optimization

This paper proposes XAL, an XML ALgebra. Its novelty is based on the simplicity of its data model and its well-defined logical operators, which makes it suitable for composability, optimizability, and semantics definition of a query language for XML data. At the heart of the algebra resides the notion of collection, a concept similar to the mathematicians monad or functional programmers comprehension. The operators are classified in three clusters: extraction operators retrieve the needed information from XML documents, meta-operators control the evaluation of expressions, and construction operators build new XML documents from the extracted data. The resulting algebra has optimization laws similar to the known laws for transforming relational queries. As a consequence, we propose a heuristic optimization algorithm similar to its relational algebra counterpart.

RAL: an algebra for querying RDF

To make the World Wide Web machine-understandable there is a strong demand both for languages describing metadata and for languages querying metadata. The Resource Description Framework (RDF), a language proposed by W3C, can be used for describing metadata about (Web) resources. RDF Schema (RDFS) extends RDF by providing means for creating application specific vocabularies (ontologies). While the two above languages are widely acknowledged as a standard means for describing Web metadata, a standardized language for querying RDF metadata is still an open issue. Research groups coming both from industry and academia are presently involved in proposing several RDF query languages. Due to the lack of an RDF algebra such query languages use APIs to describe their semantics and optimization issues are mostly neglected. This paper proposes RAL (an RDF algebra) as a reference mathematical study for RDF query languages and for performing RDF query optimization. We define the data model, we present the operators to manipulate the data, and we address the application of RAL for query optimization. RAL includes: extraction operators to retrieve the needed resources from the input RDF model, loop operators to support repetition, and construction operators to build the resulting RDF model.

Towards distributed processing of RDF path queries

A technical infrastructure for storing, querying and managing RDF data is a key element in the current semantic web development. Systems like Jena, Sesame or the ICS-FORTH RDF Suite are widely used for building semantic web applications. Currently, none of these systems support the integrated querying of distributed RDF repositories. We consider this a major shortcoming since the semantic web is distributed by nature. In this paper we present an architecture for querying distributed RDF repositories by extending the existing Sesame system. We discuss the implications of our architecture and propose an index structure as well as algorithms for query processing and optimisation in such a distributed context.

Adapting graph visualization techniques for the visualization of RDF data

The foundation language for the Semantic Web is the Resource Description Framework (RDF). RDF is intended to describe the Web metadata so that the Web content is not only machine readable but also machine understandable. In this way one can better support the interoperability of Web applications. RDF Schema (RDFS) is used to describe different RDF vocabularies (schemas), that is, the classes and properties associated to a particular application domain. An instantiation of these classes and properties form an RDF instance. It is important to note that both an RDF schema and an RDF instance have RDF graph representations. Realizing the advantages that RDF offers, in the last couple of years, many tools were built in order to support the browsing and editing of RDF data. Among these tools we mention Protégé (Noy et al., 2001), OntoEdit (Sure et al., 2003), and RDF Instance Creator (RIC) (Grove, 2002). Most of the text-based environments are unable to cope with large amounts of data in the sense of presenting them in a way that is easy to understand and navigate (Card et al., 1999). The RDF data we have to deal with describes a large number of Web resources, and can thus easily reach tens of thousands of instances and attributes. We advocate the use of visual tools for browsing RDF data, as visual presentation and navigation enables users to effectively understand the complex structure and interrelationships of such data. Existing visualization tools for RDF data are: IsaViz (Pietriga, 2002), OntoRAMA (Eklund et al., 2002), and the Protégé visualization plug-ins like OntoViz (Sintek, 2004) and Jambalaya (Storey et al., 2001). The most popular textual RDF browser/editor is Protégé (Noy et al., 2001). The generic modeling primitives of Protégé enable the export of the built model in different data formats, among which is also RDF/XML. Protégé distinguishes between schema and instance information, allowing for an incremental view of the instances based on the selected schema elements. One of the disadvantages of Protégé is that it displays the information in a hierarchical way, that is, using a tree layout (Sugiyama et al., 1981), which makes it difficult to grasp the inherent graph structure of RDF data. In this chapter, we advocate the use of a highly customizable, interactive visualization system for the understanding of different RDF data structures. We implemented an RDF data format plug-in for GViz (Telea et al., 2002), a general-purpose visual environment for browsing and editing graph data. The largest advantage that GViz provides in comparison with other RDF visualization tools is the fact that it is easily

Adaptation Control in Adaptive Hypermedia Systems

A hypermedia application offers its users a lot of freedom to navigate through a large hyperspace, described by a domain model. Adaptive hypermedia systems (AHS) aim at overcoming possible navigation and comprehension problems by providing adaptive navigation support and adaptive content. The adaptation is based on a user model that represents relevant aspects about the user. In this paper, we concentrate on the adaptation engine (AE) that is responsible for performing the adaptation according to the adaptation rules specified in the adaptation model. We analyze the dependencies between the authoring process and the functionality of the adaptation engine. From this we conclude how the authoring process can be simplified by a more powerful AE. In particular, a well-designed AE should be general purpose (i.e., not application domain specific) and should guarantee that the interpretation of the rules is deterministic, always terminates and produces the results desired by the author.

A generic component for exchanging user models between web-based systems

Educational web-based systems exemplify the increasing need for personalisation. Applications that adapt to individual users need a model of the user that contains as accurate data as possible. On the web, learners use multiple educational systems and spend their time over many applications: these are individually limited in their user modelling but can gain from joining forces. This boils down to establishing semantic interoperability of user or learner models. While semantic interoperability is hard, the emerging Semantic Web (SW) might offer just the mechanisms we need. In this paper, we develop the Generic User model Component (GUC): a generic software that utilises SW technology to support the exchange of user model data between applications. For a semantically effective user model exchange, GUC allows the configuration of a distributed management of mappings between user models. Thus, applications can choose different levels of uniting user models to maximise their personalisation.

Embedding information retrieval in adaptive hypermedia: IR meets AHA!

This paper concentrates on the retrieval aspect in adaptive hypermedia (AH). Traditionally, AH research concentrates on applications that are ‘closed’, in the sense that they assume fixed content elements. Certain applications ask for an extension of the contents considered, with data obtained through information retrieval (IR). This paper addresses this issue of ‘opening up’ AH applications, and gives insight into research that applies techniques from IR and from the Semantic Web (SW) for the embedding of IR in AH. We look at this issue in the context of an abstract reference model (AHAM) and a concrete implementation framework (AHA!). The goal of this research is to define a framework for AH with extended IR functionality. We address the relevant issues for this framework, characterized by the application of concepts from the SW paradigm leading to an enriched notion of concept relevancy.