An Active Rule Language for ROCK & ROLL

This paper presents an active rule language for the ROCK & ROLL deductive object-oriented database system. A characteristic feature of ROCK & ROLL is that it blends imperative and deductive programming styles so that both can be used together in support of passive database applications. The aim in developing an active extension is to allow declarative expression of aspects of active behaviour wherever possible, without imposing prohibitive restrictions on the power of the resulting system. The proposal which results is more powerful than most earlier declarative active rule systems, in both its language and execution model, without resorting to the wholly procedural approach supported by most proposals for active object-oriented databases. The paper indicates where retaining declarative features yields greatest beneets, but also where diiculties are encountered which lead to compromises.