부산대학교 도서관

This paper describes a unification of two different SQL extensions for streams and its associated semantics. We use the data models from Oracle and StreamBase as our examples. Oracle uses a time-based execution model while StreamBase uses a tuple-based execution model. Time-based execution provides a way to model simultaneity while tuple-based execution provides a way to react to primitive events as soon as they are seen by the system.The result is a new model that gives the user control over the granularity at which one can express simultaneity. Of course, it is possible to ignore simultaneity altogether. The proposed model captures ordering and simultaneity through partial orders on batches of tuples. The batching and the ordering are encapsulated in and can be modified by means of a powerful new operator that we call SPREAD. This paper describes the semantics of SPREAD and gives several examples of its use.