Web Services - Introduction

Today the Internet connectivity is increasing the day by day. Earlier theconnectivity was limited only to the computers that were using same hardwareand software technologies. But this limited functionality was insufficient tofulfill the ever-growing needs. So there was necessity of such kind of a systemcan allow inter platform communications, or I can say that the communicationsshould be independent of the Operating Systems and Programming Languages. Toaddress this issue the concept of web services was introduced.

A web service has list of methods and procedures that can be used by any ofthe applications irrespective of the programming languages, OS, hardware usedto develop them. Any type of applications can access the functionality providedby the web service and such functionality is called web methods or web APIs.

A web service allows the communication via internet standards XML andHTTP.Thus I, can say that any computer that has an access to the internet canhave access to the web service. Once the web service is deployed on theInternet it can be used by any of the clients using HTTP and XML. There can bea web service, which provide the details of any person based on its socialsecurity number. This service can be readily available to any clients who needto access it.

The fundamental requirements for a web service are listed as under.

• A common format for data representation so that the communication or data exchange should be platform agnostic.
• A standard specification for sending messages to web service and receiving responses from web services.
• A standard format to describe a web service.
• A standard for publishing and discovering web services enabling applications to access them.

The various requirements described above are based on the open standardssuch as XML, SOAP, WSDL and UDDI.

• Since XML (eXtensionable Markup Language) is considered as cross platform standard for transferring data over Internet because it is understand by any hardware and software. The XML also describes the data.
• In order to communicate there must be a common protocol to exchange the information. SOAP (Simple Object Access Protocol) is Microsoft implementation, responsible for transporting messages between network applications and includes protocols such as HTTP, HTTPS, SMTP and MIME. It uses the XML for information exchange. The messages received or returned by SOAP are called Request and Response envelopes. These are strictly based on XML and described in WSDL for that web service.

?????????WSDL (Web Services Description Language) describes,publicly available methods provided by the web service. The information itprovides such as the name of methods, parameters passed to the web services andthe values it returns. It is a standard for describing the web service methods.WSDL is a XML format that is used to describe web services.The following arethe elements of WSDL.

o???????definitions: This is the root element and has webservice name and its target namespace.

o???????types: This element defines the data types used by theweb services. WSDL uses W3C XML Schema syntax to define data types.

o???????message: This describes the request and responsemessages.

o???????portType: It is most important element of web service.This defines the operations such as the input and output/Request and Responsemessages involved.

o???????bindings: In bindings element we define the waymessages are transported i.e. binding style and transport protocol.

o???????documentation: It will provide the brief description ofthe service.

?????????UDDI (Universal Description, Discovery and Integration)provides a mechanism for clients to dynamically discover services available.When a service provider wants to make a web service publicly available itregisters it in UDDI directory and provides WSDL for describing the webservice.