We discuss the applicability of schema integration techniques developed for tightly-coupled database interoperation to interoperation of databases stemming from different modelling contexts. We illustrate that in such an environment, it is typically quite difficult to infer the real-world semantics of remote classes from their definition in remote databases. However, defining relationships between the real-world semantics of schema elements is essential in existing schema integration techniques. We propose to base database interoperation in such environments on instance-level semantic relationships, to be defined using what we call object comparison rules. Both the local and the remote classifications of the appropriately merged instances are maintained, allowing for the derivation of a global class hierarchy if desired.
In June 1997, an international workshop on engineering of federated database systems has been held in Barcelona in conjunction with the 9th Conference on Advanced Information Systems Engineering (CAiSE'97). This paper reports on the results of this workshop and summarises the identified open issues for future research in this area
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This paper presents techniques for reverse engineering of relational database applications. The target of such an effort is the definition of a fully equipped object-oriented view of the relational database, including methods and constraints. Such views can be seen as a full specification of the database semantics, aiding for example in the identification of semantic heterogeneity among interoperable databases. The general problem of translating from an imperative programming language environment to a declarative context such as provided by our target OODML is very hard. However, we show that the specific features of database application software allow for the development of a framework geared towards the particular problems encountered in this context.
We discuss the impact of locally implemented behavi0ur in a federation of object-oriented databases. In particular, given a specification of an integrated view of a number of component databases, we discuss the process of determining the global methods that are implicitly implemented by a given set of local methods on these component databases. To this end, we develop the notions of objectivity and sub-jecti~i~y of local methods, indicating whether the execution of a local method affects the global view exactly as it affects the local database, behaviour equivalences between local methods, indicating whether local methods of different components have similar effect, and behaviour concurrences, indicating whether local methods respond to the same event.
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