Introduction to web-services

Web-service- A web service is a method of communication between two electronic devices over the WWW. So, in web service there are two devices, namely,

• Server - Which has resource and shares it to the client.
• Client - Requests the desired resource from server.

Server provides web API (application programming interface) that is typically a defined set of HTTP request messages along with a definition of the structure of response messages, typically expressed in JSON or XML.
Example of web-services,

• Google Map.
• Blogger - Client can create, edit, view, delete and search blog's content using Blogger Data API. 
• Facebook
• Amazon
• So on...

So, requirements for web-services,

• The Web services architecture is an interoperability (The ability of software and hardware on different machines from different vendors to share data is interoperability) architecture : because client can be any device. Server must provide resource that is understood by client.  So, mostly XML (most of languages including PHP, Java, DotNet, etc can create/ read xml files), JSON (JavaScript on Notation) etc are used. 
• Server which gives resource
• Client which requests resource
• Communication to others (to application developer at client side) to use web-services. So, mostly documentation is provided by web-servers.