Retrieving time information from natural-language texts
Lynette Hirschman · 1980
An understanding of time relations is central to processing information contained in a narrative. A typical narrative is concerned with the relative ordering or progression of events over time, and the information that one would like to retrieve is often of the type 'What happened after event x?' or 'Did event x precede event y?' Determination of causality also requires a knowledge of time relations, since an event x can cause an event y only if it precedes event y in time. There has been considerable interest in the processing of time information among researchers in artificial intelligence. Several systems have been designed which compute time relations from a structured input of time specifications. Kahn and Gorry (1977) present a 'time specialist' program which accepts input about time relations in a LISP-like form; from this input, the 'specialist' comp~tes time relations, checks for inconsistencies in the input and answers questic~ns about time relations between the events given in the input. The speciali~' provides several different ways of organising the time