COLAN - A FUNCTIONAL CONSTRAINT LANGUAGE AND ITS IMPLEMENTATION

This paper is about the definition of CoLan, a high-level declarative Constraint Description Language, for use with an Object-Oriented Datab ase (OODB). CoLan has features of both first-order logic and functiona l programming and is based on Daplex. CoLan expressions are translated into Prolog code that implements the operational semantics of the con straint. Pieces of generated code are cached inside the class descript or of the 'host' class attached to appropriate slots. The pieces of co de are retrieved along an inheritance path when an update on the datab ase is attempted. If the update violates any of the retrieved constain ts then it is rejected with an informative message. Thus constraints a re expressed declaratively and they can even be retracted individually . However, they are implemented efficiently as code-generated methods, triggered selectively by an update. The implementation is described f or the ADAM OODB, which uses meta-classes of the CoLan system to gener ate class descriptions.