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Contract-to-Implementation Coupling

When details about a service's underlying implementation are embedded within a service contract, an extent of contract-to-implementation coupling is formed.

This negative coupling type commonly results when service contracts are a native part of the service implementation (as with component APIs) or when they are auto-generated and derived from implementation resources, such as legacy APIs, components, and databases.

Implementation details within a service contract result in the requirement that service consumer programs physically bind themselves to these implementation characteristics, thereby causing dependencies that will be impacted whenever the implementation changes.

The "contract first" approach dictated by modern service-oriented design processes aims to avoid contract-to-implementation coupling by ensuring the service contract is designed independently of its eventual implementation environment.

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