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A homomorphism theorem for weighted context-free grammars

✍ Scribed by Donald F. Stanat


Publisher
Elsevier Science
Year
1972
Tongue
English
Weight
731 KB
Volume
6
Category
Article
ISSN
0022-0000

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✦ Synopsis


Productions of a context-free grammar can be given coefficients from semirings, inducing weights for both derivations in the grammar and strings over the terminal alphabet. For a weighted context-free grammar in Greibach normal form, the weight of any string, as well as the set of derivations of the string, may be determined from the image under a homomorphism which maps each terminal symbol to a polynomial. The definition of the homomorphism is a straightforward function of the productions. Some examples of interesting semiring structures are included.


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A practical method is presented for the automatic generation of a non-recursive context-free grammar (cfg) from a set of strings that the cfg is required to be capable of producing. The method is efficient in computing time by comparison with enumerative methods.