Web Services Tutorial for Beginners

What is web services testing ?

Web Services  are services that are made available from a business's Web server for Web users or other Web-connected programs. Web services are also called application services.

WSDL & XML : A Web service has an interface described in WSDL( a machine-processable format ). XML is the foundation for the Web Services Description Language ( WSDL ). Web service takes the request and sends the response in the XML format.

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WebService can be called by a Software Application using SOAP or HTTP protocol.

Role of middleware : Some Web services can communicate with other services. This communication(exchange of procedures and data) is enabled by a class of software known as middleware.

Other systems interact with the Web service using SOAP (Simple Object Access Protocol) messages. SOAP messages are conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.

Web Services can be implemented any of the following two ways
  • SOAP (Simple Object Access Protocol)
  • REST (Representational State Transfer architecture)


SOAP

SOAP is a standard protocol for sending and receiving web service requests and responses. It uses the XML format to send and receive requests.
As SOAP uses the simple http transport protocol, its messages do not get blocked by the firewalls.




REST

REST means REpresentational State Transfer; it runs over HTTP. 
REST is an alternative to SOAP (Simple Object Access Protocol) and instead of using XML for request, REST uses simple URL in some cases.
Unlike SOAP, RESTFUL applications use HTTP built in headers to carry meta-information.
There are various code that RESTful applications use to determine whether user has access to API or not. These codes are
1.    200 or 201 indicates successful interaction with response body while
2.    400 indicates a bad request or the request URI does not match the APIs in the system.
All API request parameters and method parameters can be sent via either
1.    POST or 
2.    GET variables. 


Rest API supports both XML and JSON format. It is usually preferred for mobile and web apps as it makes app work faster and smoother.