View source for Temporal expressions

{{Short description|Text that denote time}}
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: 
<pre>He was born on <TIMEX>6 May, 1980</TIMEX>.</pre>
:A duration:
<pre>The show lasted <TIMEX>7 minutes</TIMEX>.</pre>
:A frequency:
<pre>The pump circulates the water <TIMEX>every 2 hours</TIMEX>.</pre>

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.<ref>See [http://timeml.org/site/publications/timeMLdocs/timeml_1.2.1.html#timex3 TIMEX3 at timeml.org]</ref>

==Approaches==
Similarly to NER systems, temporal expression taggers have been created either using linguistic [[formal grammar|grammar]]-based techniques or [[statistical model]]s. Hand-crafted grammar-based systems typically obtained better results, but at the cost of months of work by experienced linguists. There are many such systems available now,<ref>{{cite journal|last=Strötgen|first=Jannik|author2=Michael Gertz |title=HeidelTime: High quality rule-based extraction and normalization of temporal expressions|journal=Proceedings of the 5th International Workshop on Semantic Evaluation|year=2010|publisher=ACL}}</ref><ref>{{cite journal|last=Llorens|first=Hector|author2=Leon Derczynski |author3=Robert Gaizauskas |author4=Estela Saquete |title=TIMEN: An Open Temporal Expression Normalisation Resource|journal=LREC|year=2012|pages=3044–3051 |publisher=ACL|url=https://aclanthology.org/L12-1015/}}</ref><ref>{{cite journal|last=Filannino|first=Michele|author2=Gavin Brown |author3=Goran Nenadic |title=ManTIME: Temporal identification and normalization in the TempEval-3 challenge|journal=Proceedings of the 7th International Workshop on Semantic Evaluation|year=2013|publisher=ACL}}</ref> so creating a temporal expression recognizer from scratch is generally an undesirable duplication of effort. Instead, current approaches focus on novel subclasses of timex.<ref>{{cite journal|last=Brucato|first=Matteo|author2=Leon Derczynski |author3=Hector Llorens |author4=Kalina Bontcheva |author5=Christian S. Jensen |title=Recognising and Interpreting Named Temporal Expressions|journal=Proceedings of the International Conference on Recent Advances in Natural Language Processing|year=2013|publisher=ACL|url=https://aclanthology.org/R13-1015.pdf}}</ref>

Statistical systems typically require a large amount of manually [[annotation|annotated]] training data and are usually applied to the recognition task only (although there is work done using machine learning algorithms to resolve certain ambiguities in the interpretation step).<ref>See, for example, {{Harvnb|Ahn|van Rantwijk|de Rijke|2007}}</ref><ref>{{cite journal|last=Angeli|first=Gabor|author2=Christoper Manning |author3=Daniel Jurafsky |title=Parsing time: Learning to interpret time expressions|journal=Proceedings of NAACL|year=2012|page=446|publisher=ACL|url=https://aclanthology.org/N12-1049.pdf}}</ref>

== Notes ==
{{reflist}}

== References ==
* {{Citation
| first1=David | last1=Ahn | author-link=David Ahn 
| first2= Joris | last2=van Rantwijk | author2-link=Joris van Rantwijk
| first3= Maarten | last3=de Rijke | author3-link=Maarten de Rijke 
| year=2007
| journal=Proceedings of Human Language Technologies: The Annual Conference of the North American Chapter of the Association for Computational Linguistics (NAACL-HLT 2007)
| title=A Cascaded Machine Learning Approach to Interpreting Temporal Expressions
| publisher=ACL
| url=http://www.aclweb.org/anthology-new/N/N07/N07-1053.pdf}}
* {{Citation
| last1=Filannino | first1=Michele | author-link=Michele Filannino
| last2=Brown | first2=Gavin | author2-link=Gavin Brown (computer scientist)
| last3=Nenadic | first3=Goran | author3-link=Goran Nenadic
| year=2013
| title=ManTIME: Temporal identification and normalization in the TempEval-3 challenge
| journal=Proceedings of the 7th International Workshop on Semantic Evaluation
| publisher=ACL
| url=https://www.cs.york.ac.uk/semeval-2013/accepted/37_Paper.pdf}}

{{DEFAULTSORT:Temporal Expressions}}
[[Category:Computational linguistics]]
[[Category:Data modeling languages]]
[[Category:Time]]