Middleware

Distributed computing and object oriented technology have produced major shifts in the design and development of architectures for modern databases (Bancilhon et al., 1992) (Alonso et al., 1990) (Roussopoulos and Delis, 1991). A key feature of the distributed object environment is systems integration. With the advent of powerful PCs and workstations, the proliferation of information processing systems continues in all aspects of daily life. However, the wide variety of resources — in terms of both applications and supporting databases — poses a formidable challenge for system integration and interoperation (Litwin et al., 1990) (Alonso and Barbara, 1989) (Bouguettaya and King, 1993). Combination, coordination, and integration of information resources are required to meet the demands of both users and developers. In (Manola et al., 1992), two important phases for integrating resources are identified: interconnectivity and interoperability. While interconnectivity guarantees that resources can exchange messages with each other, interoperability is the mechanism which allows interaction between resources. Tools which are commonly used for such purposes are remote procedure call facilities (Bershad et al., 1987) (Notkin et al., 1988). Models of interoperability (Heimbigner and McLeod, 1985) (Sheth and Larson, 1990) (Litwin et al., 1990) include global transactional interactions and the understanding of information provided at each resource location.