The principal characteristics of SOA are described in more detail here:
SOA is a black-box component architecture. The black box lets you reuse existing business applications; it simply adds a fairly simple adapter to them. You don’t need to know every detail of what’s inside each component; SOA hides the complexity whenever possible.
SOA components are loosely coupled. Software components are loosely coupled if they’re designed to interact in a standardized way that minimizes dependencies. One loosely coupled component passes data to another component and makes a request; the second component carries out the request and, if necessary, passes data back to the first. Each component offers a small range of simple services to other components. A set of loosely coupled components does the same work that software components in tightly structured applications used to do, but with loose coupling you can combine and recombine the components in a bunch of ways. This makes a world of difference in the ability to make changes easily, accurately, and quickly.
SOA components are orchestrated to link through business processes to deliver a well-defined level of service. SOA creates a simple arrangement of components that, together, deliver a very complex business service. Simultaneously, SOA must provide acceptable service levels. To that end, the components ensure a dependable service level. Service level is tied directly to the best practices of conducting business, commonly referred to as business process management (BPM) — BPM focuses on effective design of business process and SOA allows IT to align with business processes.