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(a) To establish a theoretical framework for active rules which can be used to account for the semantics of existing systems and as a basis for developing future systems.(b) To construct a toolkit which permits experimentation with alternative strategies for optimisation and evaluation of active rules.Progress:The following progress has been made with respect to the above aims:(a) An informal framework has been developed which identifies a number of dimensions of active database functionality, and which can be used to characterise both existing systems and the requirements of applications [1]. These dimensions of active behaviour have in turn been used to direct the development of two formal frameworks for describing active database systems. The first is based upon Object-Z, and has been used to make explicit the semantics of a number of systems which has previously only been described in an informal manner [2]. The second is based on first order logic. This approach is not as comprehensive in its treatment of execution models for active database systems, but is important in establishing the semantics of active rules in relation to more established deductive techniques. (b) The active rule toolkit is being developed within the software architecture of the database system described in [3]. The toolkit will support a range of different execution models for active behaviour, as characterised by the work described at (a). An optimiser has been designed which can be used to support a wide range of transformations on the conditions of active rules, and implementation is underway. [1) N.W. Paton, O. Diaz, M.H. Williams, J. Campin, A. Dinn and A. Jaime, Dimensions of Active Behaviour, Proc 1st Int. Workshop on Rules in Database Systems, Paton, N.W. and Williams, M.H. (eds), 40-57, Springer-Verlag, 1994. [2] J. Campin, N.W. Paton and M.H. Williams, A Structured Specification of an Active Database System, Information and Software Technology, Vol 37, No l, 47-61, 1995. [3] M.L. Barja, N.W. Paton, A.A.A. Fernandes, M.H. Williams, A. Dinn, An Effective Deductive Object-Oriented Database Through Language Integration, Proc. 20th Int. Conf. on Very Large Data Bases (VLDB), J. Bocca, M. Jarke and C. Zaniolo (eds), 463-474, Morgan-KauSmann, 1994.
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