The SOA Design Patterns site (and book) has an interesting chapter on the topic of schema centralization. The recommended solution is essentially the pattern used in AIA.
1. Establish your service inventory using a top-down business process model driven approach.
2. Identify the Enterprise Business Objects (EBO) and Enterprise Business Messages (EBM).
3. Create the EBO Schema canonical definitions using the industry standards.
4. Create the Enterprise Business Services (EBS) utilizing the EBMs created above.
The Case Study section in the end is empty, but AIA could very well be its best case study!