Layered Implementation of Temporal DBMSs|Concepts and Techniques

A wide range of database applications manage time-varying data. Examples include, e.g., accounting, personnel, schedule, and data warehousing applications. At the same time, it is well-known that querying and correctly updating time-varying data is di cult and error-prone when using standard SQL. As a result of a decade of intensive exploration, temporal extensions of SQL have reached a level of maturity and sophistication where it is clear that they o er substantial bene ts over SQL when managing time-varying data. The topic of this paper is the e ective 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. This paper adopts a quite di erent approach. Speci cally, it explores the concepts and techniques involved in implementing a temporally enhanced SQL while maximally reusing the facilities of an existing SQL implementation, e.g., Oracle or DB2. The topics covered span the choice of an adequate timestamp domain that include the time variable \now," a comparison of alternative query processing architectures including a partial parser approach, update processing, and transaction processing, the latter including how to ensure ACID properties and assign correct timestamps.