1. A method, in a distributed service-oriented data processing system, for declarative service domain federation, the method comprising: receiving, in a planning engine executing on a processor of a federation server within the distributed service-oriented data processing system, a federation intent declaration comprising a federation rule, a quality-of-service policy, and a service group definition, wherein the federation intent declaration is specified using a federation console, wherein the federation rule specifies a verb, a subject, an object, and an adverb, wherein the verb specifies an action, wherein the subject specifies a set of services, wherein the object specifies a set of service domains, and wherein the adverb specifies how the declarative service domain federation is to be carried out, and wherein the quality-of-service policy describes quality-of-services capabilities by specifying service performance measurements collected by a runtime service monitoring engine and populated in a service registry of at least one service domain, wherein the quality-of-service policy describes quality-of-service requirements that specify a set of service level assurance or optimization objectives, and wherein the quality-of-service policy is stored in a Web services performance language that is compatible with an existing Web services policy framework; automatically identifying, by the planning engine, the set of services based on the service group definition, wherein the service group definition specifies a service group by at least one of explicit enumeration, a query against a set of service properties, or a union or intersection of a plurality of other service groups; automatically generating, by the planning engine, a service visibility configuration and one or more service proxies based on the federation rule and the quality-of-service policy, wherein the visibility configuration enables service consumers to interact with service providers residing in different service domains and wherein the one or more service proxies enable a service consumer in a first service domain within a plurality of service domains to access a service in a second service domain within the plurality of service domains; automatically deploying, by the planning engine, the visibility configuration to the plurality of service domains comprising the identified set of services by generating entries in the service registries of the plurality of service domains, wherein identifying the set of services comprises querying the service registries of the plurality of service domains based on the service group definition; automatically deploying, by the planning engine, the one or more service proxies to execute within connectivity middleware executing on at least one processor of the plurality of service domains within the distributed service-oriented data processing system; collecting, by the runtime service monitoring engine, performance metrics of the identified set of services; and dynamically adjusting the one or more service proxies to maintain the quality-of-service requirements specified in the quality-of-service policy based on the collected performance metrics.