Query and role playing in the association-object data model
David Rozenshtein · 1983
One of the main goals of database systems, relational systems in particular, is to provide a degree of physical data independence for users and programs. Users should need to know the exact physical storage structures to use a database, and should be protected from changes in those structures. We attempt to go a step further, to logical data independence. Traditionally, the information in relational databases was associated with both relation names and attribute names. However, because of implementation and other considerations the relations in a database are often decomposed combined into less meaningful units. We want to protect the user from these changes. Our approach resulted in the development of the Association-Object Data Model (AODM), in which the semantics of a database is associated with its attributes only. In the AODM the relationships among attributes are expressed with various devices such as associations, objects and roles. The PIQUE query language, developed for the AODM, is a concise, yet powerful, query language with natural semantics. A distinguishing feature of PIQUE is that the tuple variables in the queries are bound implicitly, and that the logical connectives or and not can affect the binding, and, therefore, take on semantic overtones.