Stream Variables: A Quick but not Dirty SQL Extension for Continuous Queries

The ability to query data streams is of increasing importance and has been identified as a crucial element for modern organizations and agencies. This paper identifies a class of useful and practical continuous queries that can be concisely modeled by a simple relational approach coupled with a simple SQL extension. It introduces the notion of a stream variable, a conceptual entity representing an ordered subset of a data stream, aggregated and attached next to a standard relational schema as a new column. A logical expression that involves the relation's attributes and the entity's methods determines whether a stream data should be added to the stream variable. The ability to define in the same query multiple, consecutive, possibly correlated stream variables allows for great flexibility in expressing complex continuous queries. We claim that such an approach presents several opportunities for efficient optimizations.