Metadata-Based Middleware for Integrating Information Systems

This work has been finished in April 1999.

Today, information systems are widely employed for administrating large amounts of data of various application areas. Due to historical, organizational, and technical reasons, their infrastructure is usually characterized by the keywords distribution and heterogeneity, in the sense that an organization comprises several physically distributed and heterogeneous information system components. In fact, particulary within an organization, such system components are frequently interrelated. To enable their cooperation and to ensure one common access, it is required to achieve interoperability and to further integrate them logically. However, distribution and heterogeneity represent the most relevant barriers against the development of interoperable, logically integrated information systems.

This thesis presents three systems realizing middleware to overcome these barriers, called COMan, IRO-DB, and OASIS. COMan integrates an object-oriented application and a relational database, providing persistence for complex objects and object-oriented manipulation of relational data. IRO-DB focuses on the integration of arbitrary relational as well as object-oriented database systems and constitutes a database federation. OASIS deals with the integration of arbitrary security concepts at an abstract description level, enabling their central monitoring and administration despite heterogeneity.

All these systems achieve logical integration. They provide transparency with respect to distribution and heterogeneity while preserving the autonomy of the system components being integrated as far a possible. To allow for a flexible and generic integration all systems realize a metadata-based approach. This metadata-based approach prevents the hard-coding and distribution of the transformation knowledge, required due to distribution and heterogeneity aspects, over various system components. Rather, it is centralized in a reified way within a repository, thus, resulting in a system able to perform the essential transformations automatically and open to adapt to changing requirements.

Based on the experience gained by developing these three systems, a criteria catalogue is developed allowing to categorize and evaluate different kinds of metadata-based middleware. The applicability of this catalogue is demonstrated by comparing the three introduced approaches by means of the proposed criteria.