Jason Bloomberg has an older article (published March 2003) that is worth mentioning again. He introduces a set of SOA principles that relate to his description of a new job role, the SOA Architect.
Jason describes SOA in a straightforward and familiar way,
"The power and flexibility that SOAs can potentially offer the enterprise is substantial. If an organization abstracts its IT infrastructure so that it presents its functionality in the form of coarse-grained services that offer clear business value, then consumers of those services (whether they are at the same company or one of that company's business partners) can access those services independent of the underlying technology issues that support them."
Jason's Principles of SOA
The business drives the services, and the services drive the technology
Business agility is a fundamental business requirement
A successful SOA is always in flux
Jason continues by comparing a SOA architecture approach to Model-Driven Architecture, and describes how a SOA Architect must take into account the Use Cases for a service when designing their SOA.