Two-dimensional specification of queries in object-oriented databases

Visual queries based on schema graphs simplify access to databases for technical and non-technical users. Unlike relational databases, in object-oriented databases, the basic entity in a query, i.e. a class, is frequently considered as a compound of several entities to which the query operations may apply, which causes the deficiency in describing an entity of designation. In this paper, we propose a visual query language object query diagram (OQD) for object-oriented databases, where a class is decomposed into a number of object sets, each of which is a set of values of one of the attributes of the other classes. By representing each class and object sets in the class using the well-known Venn diagram in a query, OQD explicitly presents all the entities to which the operations in a query can apply. We describe the syntax and semantics of OQD through a number of illustrative examples.