What"s SOA?  

First, SOA means different things to different people:

• From the point of view of a business executive and business analyst, SOA is a set of services that constitute business IT assets and can be exposed to their customers and partners, or other portions of the organization
• From the point of view of an enterprise architect SOA is an architectural style that promotes the concepts of business processes and the orchestration of enterprise-level business services. It is also a set of architectural principles, patterns and criteria which address characteristics such as modularity, encapsulation, loose coupling, separation of concerns, reuse, composability, etc.
• From the point of view of a project manager SOA is a development approach supporting massive parallel development.
• From the point of view of a tester and/or quality assurance engineer SOA represents a way to simplify overall system testing.
• From the point of view of a software developer SOA is a programming model complete with standards, tools and technologies such as Web Services.
  

Second and even more troublesome, the broader term ``software architecture'' is fuzzy and open to interpretation. People have yet to reach agreement on an universally-accepted definition for architecture alone. The Software Engineering Institute maintains a list with software architecture definitions; currently this list contains many different definitions.

In the light of these definitions, we regard SOA as an architectural style promoting the concept of using enterprise IT resources to build business-aligned enterprise services orchestrated into business-aligned processes. SOA has the following elements:

• The components of this architectural style are Enterprise Business Services. Services represent invokable software constructs that make business offering available for repeatable use. Services map between business and IT concerns, and for the most part represent stable enterprise artifacts.
• The Enterprise Business Model prescribes the Services functionality, providing the mapping between business and IT.
• Services interactions through the exchange of semantic messages with other services or with the external world in accordance to the Enterprise Business Processes. Each process orchestrates a set of services towards realizing a business objective. For the most part Business Processes represent the enterprise artifacts subject to frequent changes.

Related articles:

 SOA Patterns:Service-Oriented Decomposition