Andrew, you are very close to my understanding of SD and SC. However, OASIS SOA and me assume that the contract is a mutual agreement and it may include some consumer's policies. For example, the SC says: "I select English but with American spelling" where "American spelling" is the consumer's requirement. The provider might support this already but did not announced based on 'politically correct marketing' or it can add this feature and issue new version of the SD and satisfy the consumer in new SC.
- Michael ________________________________ From: Andrew Herbst <[email protected]> To: [email protected] Sent: Thu, December 17, 2009 8:39:56 PM Subject: [service-orientated-architecture] Descriptions vs Contracts Greetings: Another question from an SOA neophyte. Thanks for responding to my earlier questions. I suspect this question will be easy. I am not certain I understand the distinction between a “service description” and a “service contract”, in specific respect to the mechanics of interaction (I am aware that service descriptions provide other information as well). At one level, I think there is an obvious distinction – a description is a thing that characterizes one service, while the contract is an entity that governs the interaction of two (or more) services. From various sources descriptions, I read about how a contract is constituted by description documents. I find such statements a little confusing. Clearly these two notions are tightly related. In the OASIS RAF, I read this: “Recall the fundamental definition of service is a mechanism to access an underlying capability; the service description describes this mechanism and its use. It lays the groundwork for what can occur, whereas service interaction defines the specifics through which occurrences are realized.” And, of course, the contract is related to service interaction. I will venture the following answer to my own question. Can you please comment on whether I am close to capturing the “description vs contract” distinction, at least at the conceptual level, and in specific respect to matters of mechanisms of interaction: “A service description tells potential consumers about all possible mechanisms for interacting with the service. When a service consumer enters into a contract with a service provider, both parties enter into an agreement that a specific set of mechanisms will, in fact, be used” So, roughly speaking, a service description is like me announcing to the world: “I can interact in French or in English”, whereas, a service contract is like me agreeing to speak French with a specific other person in the context of some very specific interaction. I realize this is a very basic question, and it may well not really be the aim of this group to deal with such basic things. I will therefore take no offence if no one addresses this. Thanks, Andrew Herbst
