As we split our monolithic applications into right-sized units of work (services) and pull them back together again with composite applications, we realize that the sharing of assets introduces benefit (subsidized costs, consistent logic, single source of the truth, etc.) but it also introduces new pain, namely change management.
In the last few years, most large enterprises have moved to some variation of the three tiered architecture. Here, the system typically has 4 or 5 layers or tiers:
The stateful interactions that monitor the business processes have been factored out of the business logic, and distributed joins (EII) have become first-order citizens of the architecture.
More advanced Service Oriented Enterprises have adopted this tiering model as the heart of their technical service taxonomy.
This diagram depicts the relationship that services have with the composite applications that consume them. As you can see, some services are required by more than one composite application. This is a core feature of SOA - the sharing of assets across the enterprise to solutions that need them.
Modern SOA Governance practices focus on passing the 'service baton' from one group to the next while verifying that best practices are adhered to and that the baton remains in motion. This movement throughout the software life cycle is managed according to new service/operation requests as well as for change requests. The Service Life Cycle Governance and the Evolution Governance become the primary framework for monitoring change.
The needs (features and functions) of a service will vary by the consuming application. The teams that deal with each software life cycle will need to be aware of the multiple masters (or owners) that they must serve. And on occasion, we can expect that the masters will have disagreements. They will disagree on what it should do, who pays for it, when it should be rolled out, etc. These questions are at the heart of SOA Governance!
As you can see, consuming applications need to approve, prioritize, fund, plan and communicate the changes to shared services. The Service Oriented Enterprise realizes that the services are an enterprise asset, shared for the benefit of the organization. And each business or process owner will, and should, argue for their needs. Ultimately, the group needs to come together to resolve the differences.
SOA will force more occasions where departments and business units will need to find a common ground. I.T. shops have had the need to negotiate for shared infrastructure in the past. If you move forward with SOA, this activity increases significantly. There are no magic answers to SOA Governance. My only recommendation is to make sure that the tools, processes, roles and committees are in place to make the negotiation process as efficient as possible. Said another way, a competitive advantage for the Service Oriented Enterprise is the ability to efficiently negotiate differences and take action.