Object query diagram: an extended query graph for object-oriented databases

Query graph (QG) is an easy-to-use visual query language which facilitates formulating a query. Unlike relational databases, in object-oriented databases (OODBs), the basic entity of QG, i.e. a class, may consist of several entities to which the operations of a query actually apply, which causes the increase of query complexity and lack of expressiveness. We propose a visual query language object query diagram (OQD) for OODBs, where a class is specialized as a number of object sets which are the primitive entities of designation. By using the well-known Venn diagram, OQD supports the features of object-oriented data models like object identity and multivalued attributes. We describe the syntax and semantics of OQD through a number of illustrative examples