Layered Temporal DBMS’s—Concepts and Techniques

A wide range of database applications manage time-varying data, and it is wellknown that querying and correctly updating time-varying data is difficult and error-prone when using standard SQL. Temporal extensions of SQL offer substantial benefits over SQL when managing time-varying data. The topic of this paper is the effective implementation of temporally extended SQL’s. Traditionally, it has been assumed that a temporal DBMS must be built from scratch, utilizing new technologies for storage, indexing, query optimization, concurrency control, and recovery. In contrast, this paper explores the concepts and techniques involved in implementing a temporally enhanced SQL while maximally reusing the facilities of an existing SQL implementation. The topics covered span the choice of an adequate timestamp domain that includes the time variable “NOW,” a comparison of query processing architectures, and transaction processing, the latter including how to ensure ACID properties and assign timestamps to updates.