We are presenting a framework for continuous querying of time-varying streamed XML data. A continuous stream in our framework consists of a finite XML document followed by a continuous stream of updates. The unit of update is an XML fragment, which can relate to other fragments through system-generated unique IDs. The reconstruction of temporal data from continuous updates at a current time is never materialized and historical queries operate directly on the fragmented streams. We are incorporating temporal constructs to XQuery with minimal changes to the existing language structure to support continuous querying of time-varying streams of XML data. Our extensions use time projections to capture time-sliding windows, version control for tuple-based windows, and coincidence queries to synchronize events between streams. These XQuery extensions are compiled away to standard XQuery code and the resulting queries operate continuously over the existing fragmented streams.

We are addressing the efficient processing of continuous XML streams, in which the server broadcasts XML data to multiple clients concurrently through a multicast data stream, while each client is fully responsible for processing the stream. In our framework, a server may disseminate XML fragments from multiple documents in the same stream, can repeat or replace fragments, and can introduce new fragments or delete invalid ones. A client uses a light-weight database based on our proposed XML algebra to cache stream data and to evaluate XML queries against these data. The synchronization between clients and servers is achieved through annotations and punctuations transmitted along with the data streams. We are presenting a framework for processing XML queries in XQuery form over continuous XML streams. Our framework is based on a novel XML algebra and a new algebraic optimization framework based on query decorrelation, which is essential for non-blocking stream processing.