17. A non-transitory computer-readable storage device storing software comprising instructions executable by one or more computers which, upon such execution, 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.
20. The computer-readable device of claim 17 , wherein the operations comprise: identifying one or more data structure instances in the database that each specify (i) an application, and the particular one of the alternate voice command trigger terms that are each determined based at least on the voice command trigger term; requesting a selection of a particular application from among a set of applications that includes the applications specified by the one or more identified data structure instances; receiving data indicating a selection of a particular application from among the set of applications that includes the applications specified by the one or more identified data structure instances; and in response to receiving the data indicating the selection of the particular application, adjusting a strength of a relationship between the identified data structure instance that specifies the particular application and the particular one of the alternate voice command trigger terms that are each determined based at least on the voice command trigger term.