Web Services (w/s)
* is a piece of s/w that makes itself available over the internet.
* it uses a standardized XML messaging system. [sanref2]
can be defined as a service offered by an application installed on a
particular device or server to another device or client application
after communicating with each other through www (world wide web) [sanref1]
Components of w/s
1. SOAP (simple object access protocol)
2. UDDI (universal description, discovery and integration)
3. WSDL (web service description language)
* XML based protocol for accessing web services 
* slow: soap uses xml format that must b parsed to b read.
* wsdl dependent: soap uses wsdl and doesn't have any other mechnaism to discover the service 
Books:[Java Web Services: Up and Running]
References:[sanref1] [http://www.softwaretestingclass.com/what-is-web-service-how-it-is-tested/] What Is Web Service? How It Is Tested?
[sanref3] [https://www.javatpoint.com/web-services-tutorial] Web Services Tutorial