1. A method of resolving user input that crosses different application domains to identify a discourse item, the method comprising: selecting a discourse item definition associated with a first application based on user input, the discourse item definition comprising at least one defining entity that is to be used to identify a discourse item; selecting an entity definition associated with a second application based on the user input, the entity definition defining an entity that can fulfill the role of the defining entity in the discourse item definition; identifying an entity based on the entity definition and at least a portion of the user input; and identifying a discourse item based on the discourse item definition, the identified entity and the user input.