Martin Fowler - Consumer-Driven Contracts

Article by Ian Robinson describing the consumer-driven contract pattern for managing service evolution in SOA environments.

Key Takeaways

Traditional coupling: consumers validate against the provider’s full schema (XSD), coupling to the entire interface even when only a subset is used.
Provider Contract: the full published capability of the service.
Consumer Contract: one consumer’s subset of expectations — “open and incomplete” since no single consumer uses all provider functionality.
Consumer-Driven Contract: the union of all active consumer expectations — “closed and complete”; this is what the provider must not break.
Consumers should implement “just enough” validation (e.g., Schematron assertions on specific fields) rather than full-schema validation.
Pattern excavates “hidden couplings” that broad schema validation obscures.
Providers gain visibility into how consumers actually use their service; can safely change unused capabilities.
Enables impact assessment: proposed changes can be evaluated against documented consumer expectations before deployment.

High — read directly from source.