From Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Service-oriented_architecture

SOA is a paradigm for organizing and utilizing distributed capabilities that may be under the control of different ownership domains.
It provides a uniform means to offer, discover, interact with and use capabilities to produce desired effects consistent with measurable preconditions and expectations.

SOA is an architectural style rather than a product.

Service-oriented architecture (SOA) expresses a perspective of software architecture that defines the use of loosely coupled software services to support the requirements of the business processes and software users.

SOA is a design for linking computational resources, principally, applications and data, on demand to achieve the desired results for service consumers which can be end users or other services.

In an SOA environment, resources on a network are made available as independent services that can be accessed without knowledge of their underlying platform implementation. A service-oriented architecture is not tied to a specific technology and may be implemented using a wide range of interoperability standards including RPC, DCOM, ORB or WSDL.

The following guiding principles define the ground rules for development, maintenance, and usage of the SOA.
* Reuse, granularity, modularity, composability, componentization, and interoperability
* Compliance to standards (both common and industry-specific)
* Services identification and categorization, provisioning and delivery, and monitoring and tracking

The following specific architectural principles for design and service definition focus on specific themes that influence the intrinsic behaviour of a system and the style of its design:
* Service Encapsulation
* Service Loose coupling - Services maintain a relationship that minimizes dependencies and only requires that they maintain an awareness of each other
* Service contract - Services adhere to a communications agreement, as defined collectively by one or more service description documents
* Service abstraction - Beyond what is described in the service contract, services hide logic from the outside world
* Service reusability - Logic is divided into services with the intention of promoting reuse
* Service composability - Collections of services can be coordinated and assembled to form composite services
* Service autonomy – Services have control over the logic they encapsulate
* Service statelessness – Services minimize retaining information specific to an activity
* Service discoverability – Services are designed to be outwardly descriptive so that they can be found and assessed via available discovery mechanisms[5]

In addition, the following factors should also be taken into account when defining an SOA implementation:

* SOA Reference Architecture - which provides a worked design of an enterprise-wide SOA implementation with detailed architecture diagrams, component descriptions, detailed requirements, design patterns, opinions about standards, patterns on regulation compliance, standards templates etc.
* Life cycle management - introduces the Services Lifecycle and provides a detailed process for services management though the service lifecycle, from inception through to retirement or repurposing of the services. It also contains an appendix that includes organization and governance best practices, templates, comments on key SOA standards, and recommended links for more information.
* Efficient use of system resources
* Service maturity and performance
* EAI Enterprise Application Integration

One area where SOA has been gaining ground is in its power as a mechanism for defining business services and operating models and thus provide a structure for IT to deliver against the actual business requirements and adapt in a similar way to the business. The purpose of using SOA as a business mapping tool is to ensure that the services created properly represent the business view and are not just what technologists think the business services should be. At the heart of SOA planning is the process of defining architectures for the use of information in support of the business, and the plan for implementing those architectures.

Enterprise Business Architecture should always represent the highest and most dominant architecture. Every service should be created with the intent to bring value to the business in some way and must be traceable back to the business architecture.