Web Services Primer

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W3C on Web Services: A software system designed to support interoperable machine-to-machine interaction over a network

A web service is hosted remotely and can be accessed by other systems through predefined protocols for access.

Before web services came into picture following techniques were used for this sort of communication

• RPC
• DCOM
• CORBA
• Java RMI
• Socket communication
• Database based communication
• File writing and polling

Any application can be converted to web service. A web service is a self contained component which can be invoked by other applications or web services. The major advantage of a web service is reusability. Consider a banking system, A currency converter web service can be used by money transfer system, international banking system etc. However the currency converter system does not have an inkling of what these systems do with the currency data, this is called loose coupling which is a basic feature of a web service. XML+HTTP are the most popular form of web service.

A web service is OS and programming language independent. A .Net web service on windows OS can make requests to a Java Web service on Linux OS.

The basic building blocks of a web service are following XML based components

• SOAP (Simple Object Access Protocol)
• UDDI (Universal Description, Discovery and Integration)
• WSDL (Web Services Description Language)

SOAP

SOAP is a XML based message envelop which contains all the request and response data inter changed between two applications.

The SOAP message constructed by a SOAP Sender is sent to the SOAP Message Receiver. The Receiver usually processes the received message and sends a response in the form of a SOAP message back to the Sender. There may be scenarios where the Receiver might not send the response.

Click here to read more about SOAP

WSDL (Web Services Description Language)

WSDL is a XML based component used for following purposes

• Describing a web service
• Discovering a web service

UDDI (Universal Description, Discovery and Integration)

UDDI is a repository for storing the information about the web service. This information is in form of XML

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