IT思考——从SOA的定义说起

          看这本书<Service-Oriented Architecture Compass: Business Value, Planning, and Enterprise Roadmap>里面关于SOA的定义有这么几种： 

1.  A business definition: A set of business, process, organizational, governance, and technical methods to reduce or eliminate frustrations with IT and to quantifiably measure the business value of IT while creating an agile business environment for competitive advantage.
2. Another business definition (introduced by IBM): A service-oriented architecture provides the flexibility to treat elements of business processes and the underlying IT infrastructure as secure, standardized components (services) that can be reused and combined to address changing business priorities.^[1]
3. The widest technical (and rather minimalist) definition: An enterprise-wide IT architecture that promotes loose coupling, reuse, and interoperability between systems.
4. A moderately complex technical definition: An application architecture in which all functions or services are defined using a description language and have callable interfaces that are called to perform business processes. Each interaction is independent of each and every other interaction and the interconnect protocols of the communicating devices. Because interfaces are platform independent, a client can use the service from any device using any operating system in any language.
5. The least common denominator definition: A system architecture in which application functions are built as components (services) that are loosely coupled and well-defined to support interoperability and to improve flexibility and reuse.
6. The narrowest definition: SOA is a synonym for solution architectures making use of Web service technologies such as SOAP, WSDL, and UDDI. Here SOA is defined as “any product and project architecture conforming to the W3C Web services architecture (WSA).”

          在对实际商业经理人（Bussiness Executives)的调查中发现，对SOA的定义更类似于第2种，即     

A service-oriented architecture is a framework for integrating business processes and supporting IT infrastructure as secure, standardized components—services— that can be reused and combined to address changing business priorities.

       从调查中对SOA定义的倾向可以看出，SOA这样的思想发展过程中，并不希望被束缚，其他的定义没有被选中，在于它们或多或少地描述了对这个思想的具体实现方式或技术特点。但事实是:SOA仅仅是一种随需应变而产生的应用机制，这种机制是IT环境适应市场需求的需要。它强调服务，并且希望提供最大的组合性、灵活性和重用性。对需求的迎合，将商业流程细化为服务并使其服务于变化的市场环境，应该是SOA这个概念的重点，它不应局限于某种实现方式，如第4种和第6种所描述，它们都不过是狭义上的概念。对于SOA的定义的认定的过程中，我们可以发现，它也是在发展的，并且不断的从业务和IT技术两个极点寻找到平衡点,于是才有了这个选定的比较适中并关注业务和IT技术这2方面的定义。但，它不谈具体的实现，因此，SOA的定义其实是一种目标，即在走向他的过程中，尽可以顺势而为，各尽所能。

     或许当前很多人提起SOA会和一些实现方式划上等号,希望这是无意识的.要记住的是, SOA一定是海纳白川的.