Large-Scale Temporal Data Bases for Planning in Complex Domains

Abs t rac t Planning in any realistic sett ing requires the management of an enormous amount of in format ion. This in format ion is generally temporal in nature; predict i on , plan choice, and debugging all involve reasoning about t ime. The assertions manipulated by t radi t ional predicate-calculus data base systems, such as Prolog, are timelessly t rue. In the temporal data base system described in this paper, the classical data base assertion is replaced w i th the notion of a tunc token. For any given event or fact type, the data base wi l l typical ly contain a large number of t ime tokens of that type. These tokens correspond to different occasions when an event of that type occurred or a fact of that type was made true and remained so for some period of t ime. This profusion of t ime tokens of the same type presents a problem for systems supporting temporal deductions of the sort needed in planning. Many rout ine planning operations must search through the data base for tokens satisfying certain temporal constraints. To expedite these operations, this paper describes a computat ional framework in which common-sense strategies for organizing temporal facts are exploited to speed search.