17. A non-transitory computer readable storage medium having instructions stored thereon, the instructions, when executed by one or more processors, cause the processors to perform operations comprising: storing a plurality of predefined domains each representing a respective area of service offered by an intelligent automated assistant, wherein each of the predefined domains comprises a respective plurality of concepts and one or more relations relating the respective plurality of concepts, wherein each predefined domain is associated with at least one task flow specifying steps for performing a respective task in the predefined domain, and wherein each of the predefined domains is associated with a respective plurality of words relevant to the predefined domain; obtaining a text string derived from a user request, the text string including at least one or more words derived from a speech input received from a user; from the plurality of predefined domains, identifying a relevant domain for the user request based at least on respective degrees of match between the text string derived from the user request and the respective plurality of words associated with each predefined domain; and executing a task in accordance with steps specified in a task flow associated with the relevant domain, and in accordance with one or more task parameters derived from the user request.
17. A non-transitory computer readable storage medium having instructions stored thereon, the instructions, when executed by one or more processors, cause the processors to perform operations comprising: storing a plurality of predefined domains each representing a respective area of service offered by an intelligent automated assistant, wherein each of the predefined domains comprises a respective plurality of concepts and one or more relations relating the respective plurality of concepts, wherein each predefined domain is associated with at least one task flow specifying steps for performing a respective task in the predefined domain, and wherein each of the predefined domains is associated with a respective plurality of words relevant to the predefined domain; obtaining a text string derived from a user request, the text string including at least one or more words derived from a speech input received from a user; from the plurality of predefined domains, identifying a relevant domain for the user request based at least on respective degrees of match between the text string derived from the user request and the respective plurality of words associated with each predefined domain; and executing a task in accordance with steps specified in a task flow associated with the relevant domain, and in accordance with one or more task parameters derived from the user request. 18. The computer readable storage medium of claim 17 , wherein the respective plurality of words associated with each predefined domain comprises at least two respective words that each represent a concept related to the predefined domain or an entity related to the predefined domain.