An object-oriented database enables one to model complex phenomena in the real world effectively. This database is independent of the impedance-mismatch problem that is inevitable in relational databases since the data manipulation facilities are inherently designed as database programming languages. However, higher-level data manipulation facilities such as the relational calculus and relational algebra must also be supplied, so that the object-oriented database is powerful in its functionality. Generally, object-oriented query languages are complex in comparison with relational query languages because object-oriented databases should deal with complex objects and object-specific methods. In this paper, we address a formal model of object-oriented databases and attach to it a query language on the basis of this formal model.
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