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: receiving data specifying a new voice action submitted by an application developer, the data identifying (i) an application, and (ii) a voice command trigger term; validating the received data; generating a data structure instance that specifies (i) the application, (ii) the voice command trigger term, and (iii) one or more alternate voice command trigger terms that are each determined based at least on the voice command trigger term; after generating the data structure instance enabling triggering of the new voice action by a spoken utterance based at least on storing the data structure instance at a database that comprises one or more other data structure instances, wherein one or more of the other data structure instances specify (i) an application, and (ii) one or more voice command trigger terms that includes at least one voice command trigger term that is determined based at least on another voice command trigger term in the same data structure instance; after enabling triggering of the new voice action by a spoken utterance and based at least on determining that a transcription of a spoken utterance includes a particular one of the alternate voice command trigger terms that are each determined based at least on the voice command trigger term, selecting a particular data structure instance from the database that specifies the particular one of the alternate voice command trigger terms that are each determined based at least on the voice command trigger term; and identifying a particular application that is specified by the particular data structure instance.
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: receiving data specifying a new voice action submitted by an application developer, the data identifying (i) an application, and (ii) a voice command trigger term; validating the received data; generating a data structure instance that specifies (i) the application, (ii) the voice command trigger term, and (iii) one or more alternate voice command trigger terms that are each determined based at least on the voice command trigger term; after generating the data structure instance enabling triggering of the new voice action by a spoken utterance based at least on storing the data structure instance at a database that comprises one or more other data structure instances, wherein one or more of the other data structure instances specify (i) an application, and (ii) one or more voice command trigger terms that includes at least one voice command trigger term that is determined based at least on another voice command trigger term in the same data structure instance; after enabling triggering of the new voice action by a spoken utterance and based at least on determining that a transcription of a spoken utterance includes a particular one of the alternate voice command trigger terms that are each determined based at least on the voice command trigger term, selecting a particular data structure instance from the database that specifies the particular one of the alternate voice command trigger terms that are each determined based at least on the voice command trigger term; and identifying a particular application that is specified by the particular data structure instance. 14. The system of claim 11 , wherein generating the data structure instance that specifies (i) the application, (ii) the voice command trigger term, and (iii) the one or more alternate voice command trigger terms that are each determined based at least on the voice command trigger term comprises: generating one or more alternate voice command trigger terms by applying one or more synonym rules, optionalization rules, or expansion rules to the voice command trigger term.