Dynamic Modification of Continuous Queries by Using RDF Metadata of Information Sources

Continuous queries over data streams have been used in many applications. They incrementally produce their query results according to data arrival and time progress. However, existing continuous query languages strongly assume that all information sources to be accessed by queries are explicitly specified and permanently fixed. There are more sophisticated requirements such as changing information sources and rewriting filter conditions during query execution. This paper proposes a dynamic query modification scheme for continuous queries. Our continuous query language treats not only stream data from information sources, but also metadata of the information sources and queries themselves. Internally, a continuous query is represented as a dataflow, which is an RDF graph of operators. Thus, modifying a continuous query can be regarded as rewriting the corresponding RDF graph. Searching information sources which satisfy the conditions can be also regarded as searching RDF graphs descripting metadata of information sources. Our scheme achieves both continuous searching information sources and rewriting dataflows.