The Constituent Likelihood Automatic Word-tagging System (CLAWS) is a program that performs

part-of-speech tagging In corpus linguistics, part-of-speech tagging (POS tagging, PoS tagging, or POST), also called grammatical tagging, is the process of marking up a word in a text ( corpus) as corresponding to a particular part of speech, based on both its defini ...

. It was developed in the 1980s at

Lancaster University Lancaster University (officially The University of Lancaster) is a collegiate public university, public research university in Lancaster, Lancashire, England. The university was established in 1964 by royal charter, as one of several new univer ...

by the University Centre for Computer Corpus Research on Language. It has an overall accuracy rate of 96–97% with the latest version (CLAWS4) tagging around 100 million words of the

British National Corpus The British National Corpus (BNC) is a 100-million-word text corpus of samples of written and spoken English from a wide range of sources. The corpus covers British English of the late 20th century from a wide variety of genres, with the intention ...

History

A Part-Of-Speech Tagger (POS Tagger) is a piece of software that reads text in some language and assigns parts of speech to each word (and other token), such as noun, verb, adjective, etc., although generally computational applications use more fine-grained POS tags like 'noun-plural'. Developed in the early 1980s, CLAWS was built to fill the ever-growing gap created by always-changing POS necessities. Originally created to add part-of-speech tags to the LOB corpus of British English, the CLAWS tagset has since been adapted to other languages as well, including

Urdu Urdu (; , , ) is an Indo-Aryan languages, Indo-Aryan language spoken chiefly in South Asia. It is the Languages of Pakistan, national language and ''lingua franca'' of Pakistan. In India, it is an Eighth Schedule to the Constitution of Indi ...

and Arabic. Since its inception, CLAWS has been hailed for its functionality and adaptability. Still, it is not without flaws, and though it boasts an error-rate of only 1.5% when judged in major categories, CLAWS still remains with c.3.3% ambiguities unresolved. Ambiguity arises in cases such as with the word ''flies,'' and whether it should be classified as a noun or a verb. It's these ambiguities that will require the various upgrades and tagsets that CLAWS will endure.

Rules and processing

CLAWS uses a

Hidden Markov model A hidden Markov model (HMM) is a Markov model in which the observations are dependent on a latent (or ''hidden'') Markov process (referred to as X). An HMM requires that there be an observable process Y whose outcomes depend on the outcomes of X ...

to determine the likelihood of sequences of words in anticipating each part-of-speech label.

Sample output

This excerpt from

Bram Stoker Abraham Stoker (8 November 1847 – 20 April 1912), better known by his pen name Bram Stoker, was an Irish novelist who wrote the 1897 Gothic horror novel ''Dracula''. The book is widely considered a milestone in Vampire fiction, and one of t ...

's Dracula (1897) has been tagged using both the CLAWS C5 and C7 tagsets. This is what a CLAWS output will generally look like, with the most likely part-of-speech tag following each word.

Tagsets

CLAWS1 tagset

The first tagset developed in CLAWS, CLAWS1 tagset, has 132 word tags. In terms of form and application, C1 tagset is similar to

Brown Corpus The Brown University Standard Corpus of Present-Day American English, better known as simply the Brown Corpus, is an electronic collection of text samples of American English, the first major structured Text_corpus, corpus of varied genres. This ...

tags. See Table of tags in C1 tagse
here

CLAWS2 tagset

From 1983 to 1986, updated versions leading to CLAWS2 were part of a larger attempt to deal with aspects such as recognizing sentence breaks, in order to avoid the need for manual pre-processing of a text before the tags were applied, moving instead to optional manual post-editing to adjust the output of the automatic annotation, if needed. The CLAWS2 tagset has 166 word tags. See Table of tags in C2 tagse

CLAWS4 tagset

The CLAWS4 was used for the 100-million-word British National Corpus (BNC). A general-purpose grammatical tagger, it is a successor of the CLAWS1 tagger. In tagging the BNC, the many rounds of work that went into CLAWS4 focused on making the CLAWS program independent from the tagsets. For example, the BNC project used two tagset versions: "a main tagset (C5) with 62 tags with which the whole of the corpus has been tagged, and a larger (C7) tagset with 152 tags, which has been used to make a selected 'core' sample corpus of two million words." The latest version of CLAWS4 is offered by UCREL, a research center of

CLAWS5 tagset

The CLAWS5 tagset, which was used for BNC, has over 60 tags. See Table of tags in C5 tagse
here

CLAWS6 tagset

The CLAWS6 tagset was used for the BNC sampler corpus and the COLT corpus. It has over 160 tags, including 13 determiner subtypes. See Table of tags in C6 tagse
here

CLAWS7 tagset

The standard CLAWS7 tagset is used currently. It is only different in the punctuation tags when compared to the CLAWS6 tagset. See Table of tags in C7 tagse

CLAWS8 tagset

CLAWS8 tagset was extended from C7 tagset with further distinctions in the determiner and pronoun categories, as well as 37 new auxiliary tags for forms of ''be, do'', and ''have''. See Table of tags in C8 tagse
here

References

{{Reflist

External links

CLAWS part-of-speech tagger for English
Natural language processing Corpus linguistics Tasks of natural language processing Markov models Word-sense disambiguation