Web Development

Many organizations use multiple software systems for management. Different software systems often need to exchange data with each other, and a Web service is a method of communication that allows two software systems to exchange this data over the internet. The software system that requests data is called a service requester, whereas the software system that would process the request and provide the data is called a service provider.

Different software might be built using different programming languages, and hence there is a need for a method of data exchange that doesn't depend upon a particular programming language. Most types of software can, however, interpret XML-tags. Thus, Web services can use XML files for data exchange. Rules for communication between different systems need to be defined, such as:

  • How one system can request data from another system
  • Which specific parameters are needed in the data request
  • What would be the structure of the data produced. Normally, data is exchanged in XML files, and the structure of the XML file is validated against an .xsd file.
  • What error messages to display when a certain rule for communication is not observed, to make troubleshooting easier

All of these rules for communication are defined in a file called WSDL (Web Services Description Language), which has the extension .wsdl.

A directory called UDDI (Universal Description, Discovery and Integration) defines which software system should be contacted for which type of data. So when one software system needs one particular report/data, it would go to the UDDI and find out which other system it can contact for receiving that data. Once the software system finds out which other system it should contact, it would then contact that system using a special protocol called SOAP (Simple Object Access Protocol). The service provider system would first of all validate the data request by referring to the WSDL file, and then process the request and send the data under the SOAP protocol.

Web services that use markup languages

There are a number of Web services that use markup languages:

  • Web template
  • Web Services Description Language (WSDL) from the W3C
  • XML Interface for Network Services (XINS) provides a POX-style Web service specification format
  • Web Services Conversation Language (WSCL)
  • Web Services Flow Language (WSFL) (superseded by BPEL)
  • WS-MetadataExchange
  • Representational state transfer (REST) versus remote procedure call (RPC)
  • XML-RPC-XML - Remote Procedure Call