OQL: A Query Language for Manipulating Object-oriented Databases

An essential property which is desirable in a query language designed for a certain data model is that queries issued in that language must produce results that are structured and modeled using the same data msdel. A consequence of maintaining this property in a query language is that the result of a query can be used as an operand in sc+ne other query (or queries) or can bs saved as a user's view. Existing query languages that have been designed for the class of object-oriented data models do not posses this property. In this paper, we introduce the object-oriented query language (CQL), which maintains this property. An CQL query is considered as a function, which when applied to a database, returns a s&database whose structure consists of sane selected object classes and their associations. Ihe objects that satisfy the search conditions and participate in the patterns of object associations specified in the query constitute the eXtenSiOn of the resulting subdatabase. A subdatabase folms a "context" under which systemdefined and/or user defined operations can be specified and performsd. Several advanced features such as branching association patterns and set operations on subdatabases are also presented.