Understanding Web Service

There are different versions of a definition of Web Service, which basically describes the characteristics of a Web Service, which among others the following:
An application logic that can be accessed and published using the standard Internet (TCP / IP, HTTP, Web).
Described in XML format.
Identify several with Universal Resources Identifiers (URI)
Are loosely coupled, self-contained, modular and open (Nonproprietary)
Used to support the interoperability of the interaction of machine-to-machine
through the Internet / Intranet. Web services can be implemented in the internal environment (Intranet) for the needs of integration between application systems (EAI = Enterprise Application Integration) or the external environment (the Internet) to support the application for business-to-business (e-business).

Web service is a software component that is selfcontaining, self-describing, modular applications that can be published, allocated and executed on the web (wahli et al. 2006).
Web service is a technology that changed the internet capabilities by adding a web transaction capabilities, namely the ability of the web to communicate with each program pattern-to-program (P2P). The focus for this web is dominated by the communications program-to-user interaction with business-to-consumer (B2C), while the transaction will be dominated by web-to-program interaction programs with business-to-business (Gottschalk. 2002).
Figure 1 is a building block of our web service which provides long distance communication facilities between the two applications is a web service layer architecture (Tidwell, 2001).
Layer 1: Internet Protocol standard is used as a means of transport is HTTP and TCP / IP.
Layer 2: Simple Object Access Protocol (SOAP) based on XML and used for the exchange of information among a group of services.
Layer 3: Web Service Definition Language (WSDL) is used to describe the service attribute.
Layer 4: Universal Description, Discovery and Integration, which is the central directory for a description of the service.