Temporal expressions
Encyclopedia
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:
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).
-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 computational linguists. Statistical systems typically require a large amount of manually 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).
Examples:
- A point in time:
- He was born on
6 May, 1980 .
- He was born on
- A duration:
- The show lasted
7 minutes .
- The show lasted
- A frequency:
- The pump circulates the water
every 2 hours .
- The pump circulates the water
Initially, temporal expressions were considered a type of named entities and their identification was part of the named entity recognition
Named entity recognition
Named-entity recognition is a subtask of information extraction that seeks to locate and classify atomic elements in text into predefined categories such as the names of persons, organizations, locations, expressions of times, quantities, monetary values, percentages, etc.Most research on NER...
task. Since the Automatic Content Extraction program in 2004 there has been a separate task identified and called Temporal Expression Recognition and Normalisation (TERN).
Approaches
Similarly to NER systems, temporal expression taggers have been created either using linguistic grammarFormal grammar
A formal grammar is a set of formation rules for strings in a formal language. The rules describe how to form strings from the language's alphabet that are valid according to the language's syntax...
-based techniques or statistical model
Statistical model
A statistical model is a formalization of relationships between variables in the form of mathematical equations. A statistical model describes how one or more random variables are related to one or more random variables. The model is statistical as the variables are not deterministically but...
s. Hand-crafted grammar-based systems typically obtained better results, but at the cost of months of work by experienced computational linguists. Statistical systems typically require a large amount of manually annotated
Annotation
An annotation is a note that is made while reading any form of text. This may be as simple as underlining or highlighting passages.Annotated bibliographies give descriptions about how each source is useful to an author in constructing a paper or argument...
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).
External links
- TimexPortal - contains information about research on temporal expression recognition and normalisation, including annotation standards, available corpora, researchers in the field, systems and literature.
- ACE - the website of the Automatic Content Extraction program.