Pushing reactive services to XML repositories using active rules

Push technology, i.e., the ability of sending relevant information to clients in reaction to new events, is a fundamental aspect of modern information systems; XML is rapidly emerging as the widely adopted standard for information exchange and representation and hence, several XML-based protocols have been defined and are the object of investigation at W3C and throughout commercial organizations. In this paper, we propose the new concept of active XML rules for "pushing" reactive services to XML-enabled repositories. Rules operate on XML documents and deliver information to interested remote users in reaction to update events occurring at the repository site. The proposed mechanism assumes the availability of XML repositories supporting a standard XML query language, such as XQuery that is being developed by the W3C; for the implementation of the reactive components, it capitalizes on the use of standard DOM events and of the SOAP interchange standard to enable the remote installation of active rules. A simple protocol is proposed for subscribing and unsubscribing remote rules. (C) 2002 Elsevier Science B.V. All rights reserved.