Continuous querying in database-centric Web applications

Web applications are becoming increasingly database-centric. Unfortunately, the support provided by most Web sites to explore such databases is rather primitive and is based on the traditional database metaphor of submitting an SQL query and packaging the response as an HTML page. Very often, the result set is empty or contains too many records. It is up to the user to refine the query by guessing how the query constraints must be tightened or relaxed and then go through another submit/response cycle. Furthermore, once results are displayed, typically no further exploration capabilities are offered. Web applications requiring interactive exploration of databases (e.g. e-commerce) need that the above submit/response metaphor be replaced with a continuous querying metaphor that seamlessly integrates querying with result browsing. In addition to supporting queries based on predicates on attribute values, queries based on example records should also be supported. We present techniques for supporting this metaphor and discuss their implementation in a Web-based database exploration engine.