Tagging:
The descriptors are called the tags and the
automatic assignment of the descriptors to the given tokens is called tagging.
POS Tagging
The process of assigning one of the parts of
speech to the given word is called Parts Of Speech tagging, commonly referred
to as POS tagging. Parts of speech include nouns, verbs, adverbs, adjectives,
pronouns, conjunction and their sub-categories
POS Tagger
A Part-Of-Speech
Tagger (POS Tagger) is a software that reads text and then assigns parts of
speech to each word (and other token), such as noun, verb, adjective, etc., It
uses different kinds of information such as dictionary, lexicons, rules, etc.
because dictionaries
have category or categories of a particular word, that is a word may belong to
more than one category. For example, run is both noun and verb so to solve this
ambiguity taggers use probabilistic information.
There are mainly
two type of taggers:
Rule-based – Uses
hand-written rules to distinguish the tag ambiguity.
Stochastic
taggers are either HMM based – chooses the tag sequence which maximizes the
product of word likelihood and tag sequence probability, or cue-based, using
decision trees or maximum entropy models to combine probabilistic features.
Tagset
Tagger chooses
the relevant tags to attach with the words from set of tags called tagset.
Every tagger will
be given a standard tagset. The tagset may be coarse such as N (Noun), V(Verb),
ADJ(Adjective), ADV(Adverb), PREP(Preposition), CONJ(Conjunction) or
fine-grained such as NNOM(Noun-Nominative), NSOC(Noun-Sociative), VFIN(Verb
Finite),VNFIN(Verb Nonfinite) and so on. Most of the taggers use only fine
grained tagset.
Example of an English(Treebank)
tags are shown below
NLTK POS Tagging
ACKNOWLEDGEMENT
I express my profound and sincere gratitude to my mentor Dr. Anil Kumar
Singh for providing me with all the facilities and support during my winter
internship period.
I would like to thank my guide Mr. Rajesh Mundotiya for their valuable guidance, constructive
criticism, encouragement and also for making the requisite guidelines enabling
me to complete my work with utmost dedication and efficiency.
At last, I would like to acknowledge my family and friends for the motivation,
inspiration and support in boosting my moral without which my efforts would
have been in vain.
