) Philippe Picouet E.N.S.T. - Paris picouet@inf.enst.fr Victor Vianu U.C. San Diego vianu@cs.ucsd.edu Abstract A formal framework is introduced for studying the semantics and expressiveness of active databases. The power of various abstract trigger languages is characterized and related to several major active database prototypes such as ARDL, HiPAC, Postgres, Starburst, and Sybase. 1 Introduction In the past few years there has been tremendous interest in active database systems. Active databases provide "trigger systems" that execute actions in response to specified events. A wealth of active database models have been proposed and several major prototypes produced [CCCR + 90, Coh86, Han89, MD89, SKdM92, SJGP90, WF90] (see also [WCD95]). However, foundational work in this area is still scarce (e.g., see [AWH92, BM91, HJ91a]). The aim of the present paper is to develop a formal framework for active databases and use it to investigate several basic issues relating to their seman...

In this paper we present a rule language with an event based semantics that naturally embeds the behaviour of both active rules and deductive rules and conditional update streams. The language has a quite general data model that allows the definition of both flat and structured data. Language syntax and semantics are formally defined. An interpreter is then illustrated. By using several examples, we show that this language allows to express various forms of data manipulations as well as quite general triggering computations. 1 Introduction Much research focused in the recent years on enhancing the capabilities of database systems to better support new applications (like, for instance, CAD, CASE, multimedia and expert systems) retaining, at the same time, the efficient performances in managing large amounts of data shown by traditional database environments. Interesting directions of this research include the efforts aimed at enriching (both relational and complex-object) databases wit...