A Model-driven Approach for Building Distributed Ontology-based Web Applications

Author:

Richard Vdovjak

Email:

richardv-at-win.tue.nl

Advisor:

Professor Geert-Jan Houben

Award Date:

June 2005

Institution:

Technical University Eindhoven

Institution Location:

Eindhoven, The Netherlands

Web Location:

http://alexandria.tue.nl/extra2/200511532.pdf

Abstract:

The overwhelming success of the World Wide Web has caused a change in the notion of Information Systems by adopting the Web paradigm both as the delivery platform and also as the source of their data. The Semantic Web initiative opens new possibilities which the "old" World Wide Web could not deliver. It also brings, however, new set of requirements for information system design.

Designing an information system for the Semantic Web requires the use of a thorough design methodology. We propose Hera, a model-driven methodology supporting WIS design, focusing on the processes of integration, data retrieval, and presentation generation. All Hera models are based on RDF(S), the pivot language of the Semantic Web, making the methodology a suitable candidate for designing true Semantic Web Information Systems. When the content of such a system is gathered from different information sources, the specification of how data is to be retrieved requires an appropriate specification framework and a suite of tools which are able to process the designed specifications and retrieve the data as a respons to the user query.

The contribution of this thesis lies in designing the general Hera framework and in particular, providing a solution to the problem of how to specify the outline of integration of heterogeneous information sources on the Semantic Web in order to facilitate a uniform access to their distributed data. This carefully designed view of selected pieces of data coming from different sources constitutes the semantic layer of the Hera suite, which is subsequently used by other modules to deliver a tailored hypermedia presentation to the enduser. To be able to to specify the semantic layer we propose an Integration Model formalism which is able to deal with many semantic heterogeneities that frequently occur among sources on the Semantic Web.

We designed and implemented a prototype of the integration engine which serves as a backend of the Hera suite providing the semantic layer for the rest of the framework. Due to the fact that the proposed Hera architecture is modular with clearly defined interfaces built on top of the RDF foundation, the use of the integration engine is not limited solely for the Hera suite. It can also serve as a stand-alone general purpose distributed RDF query engine allowing other parties to query the semantic layer of the designed application, dus potentially extending the content available on the Semantic Web.

As the integration engine is often faced to process large amounts of RDF data, the performance becomes an important issue. Several optimization techniques were adopted to improve the speed of query processing; these include specially tailored index structures for intelligent query routing, join ordering techniques for efficient result assembly, and algebraic optimizations for improving query plans; for this a special purpose RDF algebra (RAL)was proposed.