The characterization of continuous queries

In a world where the amount of electronic information available is constantly growing, techniques to select and filter information efficiently become increasingly important. Continuous queries are a tool that allows users to monitor one or more information sources, by giving the impression that the queries are being run continually over them. In this paper, we formalize the notion of continuous queries for a wide spectrum of environments. We consider both append-only data sources and systems that allow more general data manipulation. We examine the case where the database management software may be modified as well as where we must treat it as a black box. We study the classes of queries that can be supported in each case and present efficient implementation techniques far them.