Temporal expressions

A temporal expression in a text is a sequence of tokens (words, numbers and characters) that denote time, that is express a point in time, a duration or a frequency. Examples:

A point in time:

He was born on <TIMEX>6 May, 1980</TIMEX>.

A duration:

The show lasted <TIMEX>7 minutes</TIMEX>.

A frequency:

The pump circulates the water <TIMEX>every 2 hours</TIMEX>.

Initially, temporal expressions were considered a type of named entities and their identification was part of the named entity recognition task. Since the Automatic Content Extraction program in 2004 there has been a separate task identified and called Temporal Expression Recognition and Normalisation (TERN). Timex evaluation is now evaluated in two major temporal annotation challenges: TempEval and i2b2, both of which prefer the TimeML-level TIMEX3 standard.