Ch1-Regular Expressions and Automata

Ch1-Regular Expressions and Automata - Search and Decoding...

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Search and Decoding in Speech  Recognition Regular Expressions and Automata
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February 11, 2012 Veton Këpuska 2 Outline Introduction Regular Expressions Basic Regular Expression Patterns Disjunction, Grouping and Precedence Examples Advanced Operators Regular Expression Substitution, Memory and ELIZA Finite-State Automata Using an FSA to Recognize Sheeptalk Formal Languages Example Non-Deterministic FSAs Using an NFSA to Accept Strings Recognition as Search Relating Deterministic and Non-Deterministic Automata Regular Languages and FSAs Summary
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February 11, 2012 Veton Këpuska 3 Introduction 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 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 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 In this chapter we introduce the  regular  expression , the standard notation for characterizing  text sequences. The regular expression is used for  specifying: text strings in situations like this Web-search  example, and in other  information retrieval  applications, but also plays  an important role in  word-processing,  computation of frequencies from corpora, and  other such tasks.
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February 11, 2012 Veton Këpuska 4 Introduction Regular Expressions can be implemented via  finite-state automaton . Finite-state automaton is one of the most  significant tools of computational linguistics. Its  variations: Finite-state transducers Hidden Markov Models, and N-gram grammars  Important components of the Speech Recognition and  Synthesis, spell-checking, and information-extraction  applications that will be introduced in latter chapters.
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Regular Expressions and  Automata Regular Expressions
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February 11, 2012 Veton Këpuska 6 Regular Expressions Formally, a regular expression is an algebraic notation for  characterizing a set of strings.  Thus they can be used to specify search strings as well as to define a  language in a formal way.
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This note was uploaded on 02/10/2012 for the course ECE 3541 taught by Professor Staff during the Fall '10 term at FIT.

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Ch1-Regular Expressions and Automata - Search and Decoding...

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