Querying temporal constraint networks in PTIME
Manolis Koubarakis, Spiros Skiadopoulos · 1999
We start with the assumption that temporal knowledge usually captured by constraint networks can be represented and queried more effectively by using the scheme of indefinite constraint databases proposed by Koubarakis. Although query evaluation in this scheme is in general a hard computational problem, we demonstrate that there are several interesting cases where query evaluation can be done in PTIME. These tractability results are original and subsume previous results by van Beek, Brusoni, Console and Terenziani. Introduction When temporal constraint networks are used in applications, their nodes represent the times when certain facts are true, or when certain events take place, or when events start or end. By labeling nodes with appropriate natural language expressions (e.g., breakfast or walk) and arcs by temporal relations, temporal constraint networks can be queried in useful ways. For example the query "Is it possible (or certain) that event walk happened after event breakfast...