11. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: obtaining a lexicon model that maps phones to spoken text, wherein spoken text includes only words that are spelled out; obtaining a language model that assigns probabilities to written text, wherein written text includes (i) words that are spelled out and (ii) sequences of characters that include abbreviations that are not spelled out words, acronyms that are not spelled out words, and numeric symbols; obtaining grammar rules for expanding written text into spoken text; generating, using the grammar rules, expansions of written text that includes sequences of characters that include abbreviations that are not spelled out words, acronyms that are not spelled out words, and numeric symbols into spoken text that includes only words that are spelled out, the expansions including mappings of multiple different items of written text to a particular item of the spoken text; generating a transducer that includes the expansions, where the transducer maps the written text to the spoken text, the transducer mapping the multiple different items of written text to the particular item of the spoken text; constructing a decoding network for transcribing utterances into written text, by composing the lexicon model, the inverse of the transducer, and the language model; and generating, by an automated speech recognizer, a transcription of a subsequently received utterance into written text using the decoding network.
11. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: obtaining a lexicon model that maps phones to spoken text, wherein spoken text includes only words that are spelled out; obtaining a language model that assigns probabilities to written text, wherein written text includes (i) words that are spelled out and (ii) sequences of characters that include abbreviations that are not spelled out words, acronyms that are not spelled out words, and numeric symbols; obtaining grammar rules for expanding written text into spoken text; generating, using the grammar rules, expansions of written text that includes sequences of characters that include abbreviations that are not spelled out words, acronyms that are not spelled out words, and numeric symbols into spoken text that includes only words that are spelled out, the expansions including mappings of multiple different items of written text to a particular item of the spoken text; generating a transducer that includes the expansions, where the transducer maps the written text to the spoken text, the transducer mapping the multiple different items of written text to the particular item of the spoken text; constructing a decoding network for transcribing utterances into written text, by composing the lexicon model, the inverse of the transducer, and the language model; and generating, by an automated speech recognizer, a transcription of a subsequently received utterance into written text using the decoding network. 14. The system of claim 11 , wherein the written text comprises a textual representation of a written language.