Service Oriented Architecture (SOA) is a computing paradigm which promises to provide transparency to resource access by exposing the resources available as services. SOA is based on service composition for application development and service development. Current Models for SOA describe different possible templates upon which a concrete service for SOA architecture can be built. However, with the dynamism involved in service composition, a complex service has to manage specific problems different from atomic service. This paper explores service development by proposing a composite service metamodel which addresses the requirements for constructing new services by service reuse. The composite service model handles heterogeneous constituent services and self-adaptation.