Keeping virtual information resources up and running

The maintenance of materialized views in large-scale environments composed of numerous heterogeneous information sources (ISs), such as the WWW, has importance for the new breed of information service providers. These applications face the problem that such large-scale environments are plagued with ISs not only continuously modifying their contents, but also their schemas and query capabilities. Current view technology assumes a static environment, in the sense that once the underlying environment upon which the view is deened changes its capabilities, views become undeened. This paper is the rst attempt of addressing this problem , which we coin view synchronization. Our EVE (Evolvable View Environment) solution is capable of maintaining virtual repositories (views) under capabilities changes of the underlying sources in situations where current view technology would fail. In this paper, we introduce the key concepts of the EVE solution, in particular, the EVE architecture, a new exible view speciication language called Evolvable-SQL (short E-SQL), a Model for Information Source Descriptions (MISD), and our view syn-57609. Dr. Rundensteiner would also like to thank IBM for the IBM Partnership Award as well as for providing support to this research via an IBM fellowship award to one of her graduate students Viviane Taube. Most importantly, we are grateful to our IBM collaborator Dr. Kelly Lyons and her colleagues at the Center for Advanced Studies at IBM Toronto for their encouragement , interactions, and support. chronization algorithm (VSA). Examples to illustrate the key ideas of the EVE approach are given throughout the paper.