Service isolation. This principle suggests that, to encourage service confidentiality and
loosely coupled design,4 a service??™s internal logic and the nature of its internal constituent
interactions should be ???private affairs??? and hidden from the outside world.
2. Shared knowledge. A service??™s exposed interfaces and their corresponding parameters
are the only pieces of information that a service should share with its consumers and peer
services for the purpose of interaction and message exchange.
3. Message propagation. The propagation of messages in a composite service structure
should be directed by the outermost service, meaning the containing service, downward
to its subordinate services. No outside interaction with internal service constituents is
advised. In a service cluster formation, however, the most dominant service in the cluster
group should be the propagating entity to its member services.
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234 Ch. 12 Service-Oriented Logical Design Relationship
4. Message authentication and authorization. Message exchange between services and
their consumers should be authenticated and authorized, unless an organization permits
a ???casual??? interaction style whereby contracts are not required. This scenario typically
occurs when public access is allowed.
5. Service contract. A contract is often necessary to bind consumers and services to a formal
commitment that must be enforced during the service-oriented life cycle run-time
season.
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