Question

What are the most important distinctions between services and software components?

Answer 1

Software components are under the control of the buyer of the component whereas services are controlled by the service provider. Thus, changes can be made to services without the consent of the service user.

Services are stand-alone entities that do not normally require users to make any other services available. Components may have a ‘requires’ interface that defines what other components are required to be present in the system.

Answer 2

• A critical distinction between a service and a software component is that services should be independent and loosely coupled.

• Their interface is a ‘provides’ interface that allows access to the service functionality. Services are intended to be independent and usable in different contexts. Therefore, they do not have a ‘requires’ interface.

• Software components have two related interfaces – ‘provides’ interface and ‘requires’ interface.

• Services communicate by exchanging messages, expressed in XML, and these messages are distributed using standard Internet transport protocol such as HTTP and TCP/IP. Software component can be independently deployed and composed without modification.

• There is a single standard for services against several competing standards for components so service inter-operability is much better.