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• Reusable business processes - Logic that tends to be called more than once or from more than one location should be wrapped up in a service.
   
• Self-contained - Services should be capable of performing their duties only using the supplied arguments. Thus, data stored in global variables, commons, etc., cannot be used, since this establishes a state that might not be duplicated under other conditions. In this regard, services are black boxes, engines that receive incoming data and send back a response. The same incoming data will always yield the same response.
   
• Modular - A service can rely upon other services, as long as each service follows the same key principles described in this article.

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