I know that POS tagging labels each and every word in a sentence with its appropriate Part Of Speech , But isn't that what a Parser does too ? i.e, break a sentence into its component parts? I've looked this up on the internet but couldn't find any satisfactory explanation . Please clear my doubt. Thanks in advance
They are two distinct procedures:
POS Tagging: each token gets assigned a label which reflects its word class.
Parsing: each sentence gets assigned a structure (often a tree) which reflects how its components are related to each other.
POS Tagging takes a tokenised sequence of words, and returns a list of annotated tokens, where each token has a word class label. This is often disambiguated by looking at the context surrounding the token.
There is also chunking, which groups tokens into related groups (such as noun phrases). Chunks are non-overlapping sequences.
Parsing commonly results in a parse tree for a sentence; often there can be many possible trees in case of ambiguous sentences.
POS tagging is usually a preparatory step in parsing, as a parser typically operates on word classes (though there are some parsing algorithms that work with tokens directly, or a mixture of tags and tokens).