Parsing is the term used to describe the process of automatically building syntactic analysis of a sentence in terms of a given grammar and lexicon. The resulting syntactic analysis may be used as input to a process of semantic interpretation. Occasionally, parsing is also used to include both syntactic and semantic analysis. The parsing process is done by the parser. The parsing performs grouping and labeling of parts of a sentence in a way that displays their relationships to each other in a proper way.
The parser is a computer program which accepts the natural language sentence as input and generates an output structure suitable for analysis. The lexicon is a dictionary of words where each word contains some syntactic, some semantic and possibly some pragmatic information. The entry in the lexicon will contain a root word and its various derivatives. The information in the lexicon is needed to help determine the function and meanings of the words in a sentence. The basic parsing technique is shown in figure .
Generally in computational linguistics the lexicon supplies paradigmatic information about words including part of speech labels, irregular plurals and sub categorization information for verbs. Traditionally, lexicons were quite small and were constructed largely by hand. The additional information being added to the lexicon increase the complexity of the lexicon. The organization and entries of a lexicon will vary from one implementation to another but they are usually made up of variable length data structures such as lists or records arranged in alphabetical order. The word order may also be given in terms of usage frequency so that frequently used words like “a”, “the” and “an” will appear at the beginning of the list facilitating the search. The entries in a lexicon could be grouped and given word category (by articles, nouns, pronouns, verbs, adjectives, adverbs and so on) and all words contained within the lexicon listed within the categories to which they belong. The entries are like a, an (determiner), be (verb), boy, stick, glass (noun), green, yellow, red (adjectives), I, we, you, he, she, they (pronouns) etc.
In most contemporary grammatical formalisms, the output of parsing is something logically equivalent to a tree, displaying dominance and precedence relations between constituents of a sentence. Parsing algorithms are usually designed for classes of grammar rather than tailored towards individual grammars.
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