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Service Discoverability

Table C.7. A profile for the Service Discoverability principle.
Short Definition	“Services are discoverable.”
Long Definition	“Services are supplemented with communicative meta data by which they can be effectively discovered and interpreted.”
Goals	Services are positioned as highly discoverable resources within the enterprise. The purpose and capabilities of each service are clearly expressed so that they can be interpreted by humans and software programs. Achieving these goals requires foresight and a solid understanding of the nature of the service itself. Depending on the type of service model being designed, realizing this principle may require both business and technical expertise.
Design Characteristics	Service contracts are equipped with appropriate meta data that will be correctly referenced when discovery queries are issued. Service contracts are further outfitted with additional meta information that clearly communicates their purpose and capabilities to humans. If a service registry exists, registry records are populated with the same attention to meta information as just described. If a service registry does not exist, service profile documents are authored to supplement the service contract and to form the basis for future registry records. (See Chapter 15 in SOA Principles of Service Design for more details about service profiles.)
Implementation Requirements	The existence of design standards that govern the meta information used to make service contracts discoverable and interpretable, as well as guidelines for how and when service contracts should be further supplemented with annotations. The existence of design standards that establish a consistent means of recording service meta information outside of the contract. This information is either collected in a supplemental document in preparation for a service registry, or it is placed in the registry itself. You may have noticed the absence of a service registry on the list of implementation requirements. As previously established, the goal of this principle is to implement design characteristics within the service, not within the architecture.
Web Service Region of Influence	Even though we ultimately want a discovery mechanism in place, it is also ideal for service contracts to be independently discoverable and interpretable. From a Web service perspective, this principle is focused solely on the service contract documents.

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