Difference between an SOA Service and a Web Service.

The distinction between business services or SOA services versus a web service is not often articulated, and many equate the two as being the same. SOA services can be realized as web services, but not all web services are equal to SOA services. Web services represent the use of both a published standard and a set of technologies for invocation and interoperability. SOA services are services that fulfill a key step or activity of a business process and can be described as business services and are often exposed as web services.

The picture shows the difference between SOA and web services at runtime (i.e., implementation level) and at design time. Specifically the Web Services Description Language (WSDL) and its attributes such as port types and operations. The attribute that makes it a web service is the use of WSDL or equivalent.

In design, we identify and specify a service that provides the design, or we identify and specify interfaces that include method specifications. The combination of the definition of the method and the interface at design time is what we refer to as a service from an SOA perspective. Use cases can be used to capture the functional requirements for a service.

Both SOA services and web services are part of the DNA of SOA.

In an SOA, business processes, activities, and workflow are broken down into constituent functional elements called services. They can be accessed and used directly by applications, or they can be mixed and matched with other services to create new business capabilities.

Business services or SOA services are reusable business.
Examples in banking include open account or change address. For transportation, it might be get reservation or hold reservation, and with loan processing, get loan, apply for loan, and update address are examples of business services. Business processes are also key constructs of SOA, part of its DNA.