Design and implementation of a temporal query language with abstract time

摘要

Temporal databases maintain not only current data of an enterprise but also the history of evolution for the current data (i.e. temporal data). In order to access an object from temporal databases, query languages should have facilities of specifying time. All users will use not only absolute time (e.g. July 1987) but also abstract time (or relative time) (e.g. last summer) for specifying the time that an event occurred.In this paper, we designed an extended temporal query language (ETQL) which supports both absolute time and abstract time specification. An introduction of the abstract time concept in the temporal query language provides users with friendliness and easiness in specifying time. The ETQL was implemented as front-end system on INGRES DBMS running under the 4.2BSD UNIX system.