A query model and query and knowledge definition languages for object-oriented databases
Abdallah Alashqur, Stanley Y. W. Su · University of Florida Digital Collections (University of Florida) · 1989
Maintaining the closure property is an important database language design objective. Queries issued in a query language that possesses this property return results that are structured and modeled by the same data model for which the query language is designed. A useful consequence of this is that the result of a query can be uniformly operated on by other queries (i.e., using the same language constructs). None of the existing query languages that have been designed for the class of object-oriented data models possesses the closure property. In this dissertation, we introduce a new query model for object-oriented databases in which this property is preserved. Furthermore, we make our query model concrete by introducing an object-oriented query language named OQL as an example of this query model. A query in this language returns a subdatabase whose structure consists of some selected object classes and their associations. The objects that fall in the patterns of object associations specified in the query constitute the extension of the resulting subdatabase. In this dissertation, we also introduce a knowledge definition language for defining deductive rules and integrity constraints pertaining to an object-oriented database. Deductive rules in this language derive new patterns of associations among objects based on existing and/or other derived patterns. Deductive reasoning about a large number of objects stored in a database is a needed functionality in several new database application domains (e.g., CAD/CAM databases). The OQL and the knowledge definition language are tightly coupled. This facilitates the integration of concepts and techniques, which are typically found in different categories of systems such as database management systems and expert systems, into one integrated, object-oriented knowledge base management system (OKBMS) that meets the specifications and requirements of the new database application domains.