The Enterprise Architecture concept exists for more than 20 years, but its need become urgent until recent years due to the rapid change and increasing complexity in IT, as well as the demands for business agility in Internet era. The SOA, as an architectural style, is becoming popular in architectural practice. It is moving business and IT to an integrated new paradigm. It brings new agility to EA practice, helps EA realize broader acceptance, and makes EA more usable to end-to-end enterprise solutions. Conversely, EA provides SOA practice with enterprise views as a foundation. The combination of the two benefits both business and IT for an enterprise.
It should be noticed that SOA is in a sub-domain of EA. We adopt SOA in where it applies, not practice SOA for its own sake. It's one approach after all, and many other complimentary approaches can be applied simultaneously.
The Service Oriented Infrastructure is to apply SOA to IT Infrastructure. With the changing role of IT, IT infrastructure is not only associated with hardware, software, and network components, it is becoming more integrated with business operation strategies, and being operated as a business service as well. In US Federal Enterprise Architecture program, a segmentation approach is adopted that divides the complete Enterprise Architecture domain into segments based on the identified Lines of Business (LoB), where IT Infrastructure is one of the identified LoB. The current Cloud Computing evolution is one step further, which enables a practical implementation.