Does validation mean that interface and implementation are tightly coupled, making the service hard to maintain? Mark Baker posted some more questions on validation yesterday. Validation does have merits in some cases, and the bigger challenge is designing extensible interfaces.

This post is in response to Mark Baker's post on Validation Considered Harmful. He is partly right about the harmfulness of validation in the specific use case discussed in his post, but I disagree with the generalization implied in his post. Whether validation is useful or not depends on the schema design, and document validation is not a sacred cow worth picking on.