The Internet consists of a vast collection of computers, communicating with each other to share information and provide web services to users. Each web service is derived from multiple chunks of various functionalities, working together to form such architectural design known as Service-oriented Architecture or SOA.
Web service is an example wherein SOA can be implemented to provide desired results to consumers and providers alike. It is possible that one web service needs to call for another web service in order to complete its tasks and achieve its goal at the same time. Say for example, you would like to purchase an item from an online shopping site. To do so, you need to select the product after which you will get to a page that will ask for your credit card information and other personal stuff to make the purchase. The online shopping service may have hired a third-party provider to do the online verification if indeed all the information given are valid. This is how web services and SOA work.
To make a successful interchange of information, there should be (a) a service provider, (b) a service broker and (c) a service requestor. A service provider is basically the one that creates the web service, publishing the needed information to the service registry. The service provider conceptualizes how a web service should be utilized, and what content should be exposed and made available to service requestors. A service broker, on the other hand, is the one responsible in seeing to it that all information provided by the service provider can be accessed by the service requestor. Lastly, the service requestor or client is the one that invokes the web service.