POS is the process of marking up a word in a text as corresponding to a particular part of speech, based on both its definition, as well as its context.Before we deep down to know about POS tagging its important to know about Parts of Speech.There are mainly 8 part of speech that define the words into different categories. Here is a short summary of Parts of Speech.
|part of speech||function or “job”||example words||example sentences|
|Verb||action or state||(to) be, have, do, like, work, sing, can, must||EnglishClub.com is a web site. I like EnglishClub.com.|
|Noun||thing or person||pen, dog, work, music, town, London, teacher, John||This is my dog. He lives in my house. We live in London.|
|Adjective||describes a noun||a/an, the, 69, some, good, big, red, well, interesting||My dog is big. I like big dogs.|
|Adverb||describes a verb, adjective or adverb||quickly, silently, well, badly, very, really||My dog eats quickly. When he is very hungry, he eats really quickly.|
|Pronoun||replaces a noun||I, you, he, she, some||Tara is Indian. She is beautiful.|
|Preposition||links a noun to another word||to, at, after, on, but||We went to school on Monday.|
|Conjunction||joins clauses or sentences or words||and, but, when||I like dogs and I like cats. I like cats and dogs. I like dogs but I don’t like cats.|
|Interjection||short exclamation, sometimes inserted into a sentence||oh!, ouch!, hi!, well||Ouch! That hurts! Hi! How are you? Well, I don’t know.|
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). Let’s take an example,
Input for the POS tagger be,
The strongest rain ever recorded in India shut down the financial hub of Mumbai, snapped communication lines, closed airports and forced thousands of people to sleep in their offices or walk home during the night, officials said today.
Then the output of the POS tagger should look like,
The/DT strongest/JJS rain/NN ever/RB recorded/VBN in/IN India/NNP shut/VBD down/RP the/DT financial/JJ hub/NN of/IN Mumbai/NNP ,/, snapped/VBD communication/NN lines/NNS ,/, closed/VBD airports/NNS and/CC forced/VBD thousands/NNS of/IN people/NNS to/TO sleep/VB in/IN their/PRP$ offices/NNS or/CC walk/VB home/NN during/IN the/DT night/NN ,/, officials/NNS said/VBD today/NN ./.
Here the NN tag refers to Normal Noun, JJ refers to adjective, etc,. to know more about the tags click here.