Ch1-Regular Expressions and Automata2011

Ch1-Regular Expressions and Automata2011 - Search and...

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Unformatted text preview: Search and Decoding in Speech Recognition Regular Expressions and Automata 2/13/12 Veton Këpuska 2 Outline 2/13/12 Veton Këpuska 3 Outline 2/13/12 Veton Këpuska 4 Outline Introduction u Regular Expression (RE) – is a language for specifying text search strings. n First developed by Kleene (1956) n Requires a: u Pattern – specification formula using a special language that specifies simple classes of strings. u Corpus – a body of text to search through. 2/13/12 Veton Këpuska 5 2/13/12 Veton Këpuska 6 Introduction u Imagine that you have become a passionate fan of woodchucks . Desiring more information on this celebrated woodland creature, you turn to your favorite Web browser and type in woodchuck . u Your browser returns a few sites. You have a flash of inspiration and type in woodchucks . Instead of having to do this search twice, you would have rather typed one search command specifying something like woodchuck with an optional final s . u Or perhaps you might want to search for all the prices in some document; you might want to see all strings that look like $ 199 or $ 25 or $ 24.99 . u In this chapter we introduce the regular expression , the standard notation for characterizing text sequences. The regular expression is used for specifying: n text strings in situations like this Web-search example, and in other n information retrieval applications, but also plays an important role in n word-processing, n computation of frequencies from corpora, and other such tasks. 2/13/12 Veton Këpuska 7 Introduction u Regular Expressions can be implemented via finite- state automaton . u Finite-state automaton is one of the most significant tools of computational linguistics. Its variations: n Finite-state transducers n Hidden Markov Models, and n N-gram grammars Important components of the Speech Recognition and Synthesis, spell-checking, and information-extraction applications that will be introduced in latter chapters. Regular Expressions and Automata Basic Regular Expressions 2/13/12 Veton Këpuska 9 Regular Expressions 2/13/12 Veton Këpuska 10 Regular Expressions u Formally, a regular expression is an algebraic notation for characterizing a set of strings. n Thus they can be used to specify search strings as well as to define a language in a formal way. u Regular Expression requires n A pattern that we want to search for, and n A corpus of text to search through....
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This note was uploaded on 02/11/2012 for the course ECE 5527 taught by Professor Staff during the Fall '11 term at FIT.

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Ch1-Regular Expressions and Automata2011 - Search and...

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