1. A method for building an automated assistant, the method comprising: interfacing a service-oriented architecture comprising a plurality of services to an execution environment comprising an active ontology, wherein the active ontology models a domain and comprises a logical arrangement of a plurality of active processing elements, wherein each active processing element is configured to receive at least one fact relating to the modeled domain and to perform at least one action responsive to at least one received fact; and registering at least one of the plurality of services for use in the domain, by specifying at least one of: one or more active processing elements that the at least one of the plurality of services can accept; and one or more active processing elements that the at least one of the plurality of services cannot accept; wherein: at least one of said interfacing and said registering is performed using a processor; and the active ontology filters requests for services to the at least one of the plurality of services in accordance with the one or more active processing elements specified by the at least one of the plurality of services.