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| − | Formally, a '''grammar''' is an ordered fourtuple ''G'' = (''T,N,S,P''), where ''N'' and ''T'' are finite alphabets, ''S'' is a distinguished symbol of ''N'', and ''P'' is a finite non-empty set pairs (L,R) such that ''L'' and ''R'' are in (''N U T'')* and ''G'' is called a '''Context Free Grammar''' (CFG) if ''L'' is in ''N''.
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| − | The symbols of ''N'' are called ''nonterminal symbols''. The symbols of ''T'' are called ''terminal symbols''. According to above definition of a grammar ''G'', the sets ''N'' and ''T'' are disjoint in every grammar. The nonterminal symbol ''S'' is called the initial symbol, axiom or root, and is used to start the derivations of the sentences of the language.
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| − | The ordered pairs in ''P'' are called ''rewriting rules'' or ''productions'' and will be written in the form L ---> R where the symbol ---> (derives) is, of course, not in ''N U T''. Productions are used to derive new sentences from given ones by replacing a part equal to the left-hand side of a rule by the right-hand side of the same rule.
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| − | In such a way, taking always ''S'' as the starting symbol, it is possible to derive from ''S'' and just applying productions in ''P'', a set (possibly infinite) of sentences that is called the language generated by ''G'', ''L(G)''.
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| − | '''See following grammar example:''' [http://eplmediawiki.di.uminho.pt/uploads/NLPDgrammar.pdf nLPD grammar]
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| − | [[Category: Basic Concepts]]
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Revision as of 00:52, 22 April 2013
Haha, shouldn't you be charging for that kind of knolwdege?!
