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Speech Recognition Grammar Specification
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<p>Speech Recognition Grammar Specification (SRGS) is a <a href="/facts/W3C/lGWmhF6M">W3C</a> standard for how <i><a href="/facts/Speech_recognition/z7S7Pgk6">speech recognition</a> grammars</i> are specified. A speech recognition grammar is a set of word patterns, and tells a speech recognition system what to expect a human to say. For instance, if you call an <a href="/facts/Automated_attendant/xD5Pf6qq">auto-attendant</a> application, it will prompt you for the name of a person (with the expectation that your call will be transferred to that person's phone). It will then start up a speech recognizer, giving it a speech recognition grammar. This grammar contains the names of the people in the auto attendant's directory and a collection of sentence patterns that are the typical responses from callers to the prompt. </p><p>SRGS specifies two alternate but equivalent syntaxes, one based on <a href="/facts/XML/clNgUfWk">XML</a>, and one using augmented <a href="/facts/Backus%25E2%2580%2593Naur_form/xbMXDntc">BNF</a> format. In practice, the XML syntax is used more frequently. </p><p>Both the ABNF and XML form have the expressive power of a <a href="/facts/Context-free_grammar/yu1FFdK4">context-free grammar</a>. A grammar processor that does not support recursive grammars has the expressive power of a <a href="/facts/Finite-state_machine/GMusWd0a">finite-state machine</a> or <a href="/facts/Regular_expression/KFL3veHX">regular expression</a> language. </p><p>If the speech recognizer returned just a string containing the actual words spoken by the user, the voice application would have to do the tedious job of extracting the semantic meaning from those words. For this reason, SRGS grammars can be decorated with <i>tag</i> elements, which when executed, build up the semantic result. SRGS does not specify the contents of the tag elements: this is done in a companion W3C standard, <a href="/facts/Semantic_Interpretation_for_Speech_Recognition/Xo1NhSuJ">Semantic Interpretation for Speech Recognition</a> (SISR). SISR is based on <a href="/facts/ECMAScript/M7nDHsB5">ECMAScript</a>, and ECMAScript statements inside the SRGS tags build up an ECMAScript semantic result object that is easy for the voice application to process. </p><p>Both SRGS and SISR are W3C Recommendations, the final stage of the W3C standards track. The W3C <a href="/facts/VoiceXML/jPrJ1goR">VoiceXML</a> standard, which defines how voice dialogs are specified, depends heavily on SRGS and SISR. </p>