CoLan

CoLan is a high-level declarative Constraint Description Language, for use with an Object-Oriented Database (OODB). CoLan has features of both first-order logic and functional programming and is based on Daplex. CoLan expressions are translated into Prolog code that implements the operational semantics of the constraint. Pieces of generated code are cached inside the class descriptor of the 'host' class attached to appropriate slots. The pieces of code are retrieved along an inheritance path when an update on the database is attempted. If the update violates any of the retrieved constraints then it is rejected with an informative message. Thus constraints are expressed declaratively and they can even be retracted individually. However, they are implemented efficiently as code-generated methods, triggered selectively by an update.

CoLan has been implemented in two systems: a) in ADAM OODB, which uses meta-classes of the CoLan system to generate class descriptions, and b) in P/FDM, with changes to meta-data.

• Click here to download the source files.

Relevant Publications

• N. Bassiliades, "Constraint Description in ADAM", Master thesis for the fulfillment of MSc in Applied Artificial Intelligence, September 1992.
• S.M. Embury, P.M.D. Gray and N. Bassiliades, "Constraint Maintenance Using Generated Methods in the P/FDM Object-Oriented Database", in N.W. Paton and M.H. Williams (Eds.), Rules in Database Systems: Proceedings of the 1st International Workshop on Rules in Database Systems, Edinburgh, Scotland, 30 August- 1 September 1993, Workshops in Computing Series, Springer-Verlag, 1994, pp. 364-381.
• N. Bassiliades and P.M.D. Gray, "CoLan: A Functional Constraint Language and Its Implementation", Data & Knowledge Engineering, Vol. 14, No. 3, February 1995, pp. 203-249.

For any comments regarding this page contact Nick Bassiliades.