An object-oriented structured query language and its translation to a formal algebra

Abstract

A declarative query capability has been accepted as a fundamental feature of any database management system. This thesis proposes an extension of the standard query language SQL, SQL/OO, designed for querying object-oriented databases. It has additional constructs to deal with the rich data model introduced by object-orientation. SQL/OO rests on a formal object-oriented query algebra that is highly expressive and open to optimization. Formal definitions of syntax and semantics are presented. The mapping of SQL/OO queries into object algebra is provided by a syntax-directed translation scheme. A prototype system that evaluates SQL/OO queries is designed. The system starts with a translator that translates an SQL/OO query into an equivalent object algebra expression. This algebra expression is parsed and an Object Algebra Tree (OAT) is generated which will be used as the internal representation. OAT Trees can be used as the input and output of a query optimizer module. The result of the query will be evaluated by traversing the tree and evaluating each node using proper functions that execute object algebra operations. A survey of existing object-oriented query languages in the literature is also provided. Their characteristics are identified, compared and contrasted, in order to present the necessary background.