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Technical Report HW-MACS-TR-0042

TitleCondensative Stream Query Language for Data Streams
AuthorsLisha Ma, Hamish Taylor
AbstractOver a traditional DBMS (Database Management System), the answer to an aggregate query is usually much smaller than the answer to a similar non-aggregate query. Therefore, we call such query processing condensative. Current proposals for declarative query languages over data streams do not support such condensative processing. In order to make existing stream query languages more expressive, we propose a new data stream model, referred to as the sequence model, and a novel stream query language CSQL (Condensative Stream Query Language). We show that the sequence model supports precise tuple- based semantics that is lack in previous time-based model. Moreover CSQL processes a declarative semantics that allows one to specify and reason about the diŽerent meanings of the frequency by which a query returns answer tuples, which are beyond previous query languages over streams. In addition, a novel condensative stream algebra is defined by extending the existing stream algebra with a new operator, frequency operator, to capture the condensative property. We show that a condensative stream algebra enables the generation of efficient continuous query plans, and can be used to validate query optimisation.


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