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Web Services and standard web protocols

Author: Mike Green

Web services gain more popularity from last few years in developers and companies. So there are good reasons to understand internals of Web Services.

What are Web Services?
Web Service is an application designed to directly interact with other applications all over the world on internet. It describes a standardized way of integrating web based applications. Web services allow different applications from different sources to communicate with each other.
Web Services provides an important way for business to communicate with clients and with each other. It provides business logic processes and data through a programmatic interface instead of any traditional user interface. User interface is then added to this application interface to provide specific functionality to users. The basic purpose of Web Service is to provide some functionality from the owner to its clients so that they can use it.

Web Services publish their methods to the world and these methods, when invoked, perform some actions and provide some data in result. Web services sometimes called Application Services.

Independent of Operating System and Language
Web Services are XML based applications that use XML to communicate with other applications so Web Services are independent of Operating System and Programming Language.  An application using a Web Service is not concerned about the operating system or programming language of that Web Service as all communication is in XML. For example, A Web Service created in Java can be used by an application created in Visual Basic or Windows application can be called by a UNIX application.
Web Services Protocols
Web services use XML based web protocols that include HTTP, XML, SOAP, WSDL and UDDI. XML is used to tag the data, SOAP is used to transfer data, WSDL is used to describe available Web Services and UDDI is used to list the available Web Services.
Hypertext Transfer Protocol (HTTP) is the standardized protocol of communication on the internet by the World Wide Web Consortium (W3C). It is responsible for requesting and transmitting data over the internet. It provides safe recognition of network web server and encrypted communication.
Extensible Markup Language (XML) is the markup language that is designed to transport and store data in a format that is readable by both human and machine. It enables the transmission, validation and interpretation of data between applications. . XML is used to tag, format and display the data. It allows developers to create their own customized tags. It mainly designed for documents but it is extensively used in Web Services. It is the most common markup language in which the information is written.
Simple Object Access Protocol (SOAP) is the XML based protocol to transfer the data in Web Services. It is the language and platform independent protocol that allows applications in Web Services to communicate via standard internet HTTP. It is the center piece of Web Services and complements all other protocols (XML, WSDL and UDDI). In a simple way, we can say that SOAP is the way in which web services method calls are translate into XML format and sent via HTTP and it allows applications to exchange information over HTTP. SOAP is standardized and recommended by W3C.
Web Services Description language (WSDL) is a standard format to describe and locate web services. It is the XML based language that UDDI uses for Web Services. Every client application that is connected to Web Service can read the WSDL to determine what functions are available on the Web Service. Any special data types are embedded in the WSDL. URL from which Web Service methods can be accessed and communication protocols used by web services are also in the WSDL file. So it contains every detail to allow users to build client applications to use Web Services. WSDL is the W3C recommendation.
Universal Description, Discovery and Integration (UDDI) is the web based directory or registry for listing web services. It enables businesses to list themselves on the internet and discover each other. It allows clients to find Web Services to use them. It is a public library where we can publish Web Services and inquire about Web Services. UDDI includes several ways to find Web Services that client needs to built their application.
UDDI registry manages information about service providers and service implementations. Service providers can use UDDI to publicize web services they offer and service clients can use UDDI to discover Web Services according to their requirements. UDDI is based on XML and SOAP standards.
Criticism on Web Services
Web services are often criticized because of security issues. It is the application to application interaction instead of human-application interaction. Issues like authentication, privacy and data integrity are main concerns when using Web Services. Another criticism on Web Services is the complexity in Web Services.
Benefits of Web Services
Although there are some criticisms on Web services but benefits of Web Services have overpowered these criticisms. The communication between applications is easier with Web Services. Information distribution to different clients and consumers is relatively simple task for companies. Web services can be reused when needed and from the past few years there is rapid development in Web Services. 
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