SEMANTICS-BASED TIME-ALIGNMENT OPERATIONS IN TEMPORAL QUERY-PROCESSING AND OPTIMIZATION

In a temporal database, object properties and associations evolve very irregularly in time. Different evaluations of data objects with diffe rent valid intervals need to be recorded and processed for different t emporal instances and their associations. Their intervals need to be a ligned in order to find the common intervals in which the combined dat a are valid. Efficiency can be gained if, in every step of the travers als and manipulations, a minimal number of temporal instances is produ ced. This paper presents a set of semantics-based time-alignment opera tions defined as time-computation construct. They can be used as guide s to determine the proper alignment operations that should be used to achieve efficient query processing. Five primitive time-alignment oper ations are defined in this paper. They can be combined and used to eff iciently support different temporal query situations. As a byproduct o f implementing a parallel temporal query processor on an nCUBE2 comput er, we found that these time-alignment primitives and their combinatio ns can be implemented efficiently using a memory mapping technique. We present this implementation technique and analyze its order of comple xity. (C) Elsevier Science Inc. 1997.