At last, a breath of fresh air in SOA-land! It is about time that definitions were put together by practitioners, rather than hype-merchants and people with hammers who think that everything is a nail. 
 
I have just 2 problems: 
- the word 'abstract' in the definition of interface is capable of being interpreted in many ways beside the intended one; additionally, the interface is concerned with the inputs and the outputs only, not the teleological aspects of the service. Suggestion: An interface is a machine-readable description of the structures and semantics of the inputs and corresponding outputs of the service, provided in such a way that it can be used by software on - in principle - any device to make use of the service. 
- the definition of contract does not indicate what the minimum expression is that is required in order for it to be a contract. Clearly there are expressions of Service Behavior that are inadequate, such as "The service will generally reply sometime." The sentence which follows the definition is much better: it mentions as essential ingredients the interfaces, additional requirements and agreement between the client and the service. 
 
Regards, 
 
Hans Wierenga