Supporting semantic rules by a generalized event/trigger mechanism
Non-standard applications like CAD/CAM, image processing and AI require database systems with facilities to handle sophisticated semantics. Advanced data models supporting complexly structured objects, abstract data types and the like have been developed to this end. However, any data model remains necessarily restricted to rather static and global semantics, not taking into account individual and dynamically changing issues. It is therefore necessary to formulate additional semantic rules, which may be rather complex and pose a variety of checking as well as enforcement requirements.
In this paper we present a generalized event/trigger concept as a basic support mechanism for semantic rules, which allows for flexible checking times and arbitrary actions in case of rule violation. If necessary, the user is able to control the supervision of semantic rules dynamically. Several levels of local and global rules are supported, existing algorithms for rule checking/enforcement can be integrated, and specific rules governing complex engineering processes (so-called action plans) can be dealt with. The usefulness of the mechanism is demonstrated by a number of examples.
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