Web Service

Web services represent a communication mechanism between applications remotely through the Internet network independent of any programming language and any platform performance:

1.Using the HTTP protocol as a means of transport. Thus, communications are carried out on a universal, and generally controlled unfiltered by firewalls;
2.Employing a syntax notation based on XML to describe the function calls and remote data exchanged;
3.Organizing mechanisms call and response.

Thanks to Web services, applications can be seen as a set of business services, structured and correctly described, according to a dialogue rather than an international standard set of objects and methods intertwined.

The first benefit of this cutting is the easy maintenance of the application, and interoperability can easily change a component (a service) and replace it with another, possibly developed by one third. In addition, web services can reduce the complexity of an application because the developer can focus on one service, regardless of the rest of the application.

Web services not only facilitate exchanges between enterprise applications but also allow an opening to other companies. The first web service providers are providers of online services (weather, stock exchange, route planning, yellow pages, etc..), Providing developers API (Application Programmable Interface) paid or not, allowing d ' integrate their service with third-party applications.

Layers

The functioning of Web services based on a model in layers, including the three basic layers are as follows:

Standards

The basic standards used by Web-Services (SOAP, WSDL) are standardized by the W3C (http://www.w3.org/2002/ws/), while OASIS is responsible for standardization of the upper layers , Closer to the application level (security).

Invocation

There are two major Web services standards, both based on XML:

1.XML-RPC (XML Remote Procedure Call), the oldest operating on a principle proc &evacuate; dual and without management statements.
2.SOAP (Simple Object Access Protocol), operating under the object model.
Whatever the standard used, the principle of programming is the same: calling remote method is achieved through a library client that transmits the application service provider in the formatting XML in a transparent manner; level server library decodes the application server, the server is its treatment, and then responds through the same library, the library finally score decodes the response so that it can be used by the client application.

Discovery

The most standard protocol used for the discovery of services is UDDI. The standard UDDI (Universal Description Discovery and Integration) defined by the OASIS aims to describe a standard way to publish and interrogate web services offered by a network, usually within a directory service listing services web the organization.

Description

The standard protocol used most to describe services is WSDL.The standard WSDL (Web Service Description Language) is a language based on ratings XML to describe web services. WSDL is used to describe the location of web service and operations (methods, parameters and return values) that the service provides.

Structure of a WSDL document:
A WSDL document is an XML format using the following elements:
PortType defining the web service, in particular transactions they carry out and the type of messages exchanged.
Message, including one or several parties representing the input parameters.
Types, defining the types of data used by the web service.
Binding, specifying the protocol and message format.

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