Supporting views in data stream management systems

Due to their effectiveness, views are attractive to data stream management systems (DSMSs). Prior work on languages to express continuous queries over data streams has defined a stream as a sequence of tuples that represents an infinite append-only relation. This dissertation shows that composition of queries, and hence supporting views, is not possible in the append-only stream model. Then, the dissertation proposes the Synchronized SQL (or SyncSQL) query language that defines a data stream as a sequence of modify operations against a relation. SyncSQL enables query composition through the unified interpretation of query inputs and outputs. An important issue in continuous queries over data streams is the frequency by which the answer gets refreshed and the conditions that trigger the refresh. Coarser periodic refresh requirements are typically expressed as sliding windows. In this dissertation, the sliding-window approach is generalized by introducing the synchronization principle that empowers SyncSQL with a formal mechanism to express queries with arbitrary refresh conditions. After introducing the semantics and syntax, we lay the algebraic foundation for SyncSQL and propose a query matching algorithm for deciding containment of SyncSQL expressions.;Then, the dissertation introduces the Nile-SyncSQL prototype to support SyncSQL queries. Nile-SyncSQL employs a pipelined incremental evaluation paradigm in which the query pipeline consists of a set of differential operators. A cost model is developed to estimate the cost of SyncSQL query execution pipelines and to choose the best execution plan from a set of different plans for the same query. An experimental study is conducted to evaluate the performance Nile-SyncSQL . The experimental results illustrate the effectiveness of Nile-SyncSQL and the significant performance gains when views are enabled in DSMSs.;Sliding-window queries form a special class of SyncSQL queries in which tuples expire in a First-In-First-Out (FIFO) order. The last part of the dissertation proposes optimization techniques to enhance the performance of sliding-window queries inside Nile-SyncSQL. The optimization techniques are based on the FIFO property and focus on reducing the overhead of processing the expired tuples. The experimental results illustrate the performance gains of Nile-SyncSQL when accompanied with the proposed optimizations over other sliding-window query processing approaches.