- The first step in any semantic processing system is to look up the individual words in a dictionary (or lexicon) and extract their meanings.
- Many words have several meanings, and it may not be possible to choose the correct one just by looking at the word itself.
- The process of determining the correct meaning of an individual word is called word sense disambiguation or lexical disambiguation.
- It is done by associating, with each word in the lexicon, information about the contexts in which each of the word’s senses may appear.
- Sometimes only very straightforward info about each word sense is necessary.
- Some useful semantic markers are :
- Several approaches to the problem of creating a semantic representation of a sentence have developed, including the following:
- Semantic grammars, which combine syntactic, semantic and pragmatic knowledge into a single set of rules in the form of grammar.
- Case grammars, in which the structure that built by the parser contains some semantic information, although further interpretation may also be necessary.
- Conceptual parsing, in which syntactic and semantic knowledge combined into a single interpretation system that driven by the semantic knowledge.
- Approximately compositional semantic interpretation, in which semantic processing applied to the result of performing a syntactic parse.
- A semantic grammar is a context-free grammar in which the choice of non-terminals and production rules governed by semantic as well as syntactic function.
- There is usually a semantic action associated with each grammar rule.
- The result of parsing and applying all the associated semantic actions is the meaning of the sentence.
- Advantages of Semantic grammars
- When the parse complete, the result can use immediately without the additional stage of processing that would require if a semantic interpretation had not already performed during the parse.
- Many ambiguities that would arise during a strictly syntactic parse can avoid since some of the interpretations do not make sense semantically and thus cannot generate by a semantic grammar.
- Syntactic issues that do not affect the semantics can ignore.
- The drawbacks of the use of semantic grammars are:
- The number of rules required can become very large since many syntactic generalizations missed.
- Because the number of grammar rules may be very large, the parsing process may be expensive.
- Case grammars provide a different approach to the problem of how syntactic and semantic interpretation can combine.
- Grammar rules written to describe syntactic rather than semantic regularities.
- But the structures the rules produce correspond to semantic relations rather than to strictly syntactic ones.
- Conceptual parsing is a strategy for finding both the structure and meaning of a sentence in one step.
- Moreover, Conceptual parsing driven by the dictionary that describes the meaning of words in conceptual dependency (CD) structures.
- The parsing is similar to case grammar.
- CD usually provides a greater degree of predictive power.