TypEx : a type based approach to XML stream querying
George Russell, Mathias Neumüller, Richard Connor · Strathprints: The University of Strathclyde institutional repository (University of Strathclyde) · 2003
We consider the topic of query evaluation over semistructured information streams, and XML data streams in particular. Streaming evaluation methods are necessarily eventdriven, which is in tension with high-level query models; in general, the more expressive the query language, the harder it is to translate queries into an event-based implementation with finite resource bounds. We consider an alternative model by introducing a twophase evaluation strategy. A query Q is decomposed into an event driven primary filter query Q ′ , which incrementally gathers relevant data from the input stream, and another query Q ′ ′ which consumes this data as it becomes available. Evaluation of Q(s) isthenequivalenttoQ ′ ′ (Q ′ (s)). The importance of the separation is that it allows the first