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

Author:

Flavius Frasincar

Email:

flavius_frasincar-at-yahoo.com

Advisor:

Professor Paul De Bra and Professor Geert-Jan Houben

Award Date:

June 2005

Institution:

Eindhoven University of Technology

Institution Location:

Eindhoven, The Netherlands

Web Location:

http://alexandria.tue.nl/extra2/200511530.pdf

Abstract:

Due to Web popularity many information systems have been made available through the Web, resulting in so-called Web Information Systems (WIS). Due to the complex requirements that WIS need to fulfill, the design of these systems is not a trivial task. Design methodologies provide guidelines for the construction of WIS such that the complexity of this process becomes manageable. Based on the separation-of-concerns principle some of these methodologies propose models to specify different aspects of WIS design.

Model-driven WIS design methodologies have been recently influenced by emerging technologies like the ones provided by the Semantic Web. We call WIS that use Semantic Web technologies Semantic Web Information Systems (SWIS). Hera is a SWIS design methodology that employs RDF, the foundation language of the Semantic Web, for its model representation. Using a standardized language to represent models fosters application interoperability. There are two main phases in Hera: the data collection phase, which makes available data coming from different possibly heterogeneous sources, and the presentation generation phase, which builds Web hypermedia presentations based on the previously integrated data. This dissertation concentrates on the presentation generation phase of the Hera methodology.

The presentation generation phase of the Hera methodology identifies the following design steps:

• conceptual design: constructs the conceptual model (CM), a uniform representation of the application's data. It defines the concepts and the concept relationships that are specific to the application's domain.
• application design: constructs the application model (AM), the navigational structure over the application's data. It defines slices and slice relationships. A slice is a meaningful presentation unit of some data. There are two types of slice relationships: navigation relationships, used for links between slices, and aggregation relationships, used for embedding a slice into another slice.
• presentation design: constructs the presentation model (PM), the look-and-feel specifications of the presentation. It defines regions and region relationships. A region is an abstraction for a rectangular area on the user display where the contents of a slice are presented. As for slices, there are two types of region relationships: navigation relationships, used for links between regions, and aggregation relationships, used for embedding a region into another region. Regions have associated layout (positioning of inner regions inside a region) and style (fonts, colors, etc.) information.

There are two types of presentation adaptation supported in the presentation generation phase of Hera: static adaptation, i.e., adaptation performed before the user starts browsing, and dynamic adaptation, i.e., adaptation performed while the user is browsing. The static adaptation is based on appearance conditions for elements in the CM, AM, and PM. These conditions use data from a user profile (UP) which stores the static user preferences and device capabilities. The dynamic adaptation uses AM queries in order to update the user session (US). US stores dynamic data, i.e., data created during user browsing based on user's input. The presentation generation process uses data from US in a similar way as the CM. Based on these two types of adaptation there are two variants of Hera's presentation generation phase: the static variant and the dynamic variant.

A CASE tool, the Hera Presentation Generator (HPG) supports the presentation generation phase of Hera. There are two variants of the HPG, HPG-XSLT, which corresponds to the static variant of Hera's presentation generation phase, and HPG-Java, which corresponds to the dynamic variant of Hera's presentation generation phase. HPG-XSLT implements the data transformations using XSLT stylesheets, and HPG-Java implements the data transformations in Java using Jena and Sesame libraries. HPG-Java exploits more of the RDF model semantics than HPG-XSLT. A distributed architecture of the HPG based on Web Services is also provided.