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A Web service is a service offered by an electronic device to another electronic device, communicating with each other via the World wide web. In a web service, web technology such as the HTTP protocol, originally designed for human-to-machine communication, is utilized for machine-to-machine communication, more specifically for transfering machine readable file formats such as XML and JSON. In practice, the web service typically provides an object-oriented web based interface to a database server, utilized for example by another web server, or by a mobile application, that provides a user interface to the end user. Another common application offered to the end user may be a mashup, where a web server consumes several web services at different machines, and compiles the content into one user interface. The W3C defines a Web service generally as: In a 2002 document, the (W3C Web Services Architecture Working Group ) defined a Web Services Architecture, requiring a standardized implementation of a "Web service." In this: In a 2004 document, the W3C extended the definition: == Explanation == The term "Web services" describes a standardized way of integrating Web-based applications using the XML, SOAP, WSDL and UDDI open standards over an Internet protocol backbone. XML is used to tag the data, SOAP is used to transfer the data, WSDL is used for describing the services available and UDDI lists what services are available. A Web service is a method of communication between two electronic devices over a network. It is a software function provided at a network address over the Web with the service ''always on'' as in the concept of utility computing. The W3C defines a Web service generally as: a software system designed to support interoperable machine-to-machine interaction over a network. 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 may use 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 a .wsdl extension. (Proposals for Autonomous Web Services (AWS) seek to develop more flexible web services which do not rely on strict rules.〔Compare: 〕) 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 validate the data request by referring to the WSDL file, and then process the request and send the data under the SOAP protocol. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Web service」の詳細全文を読む スポンサード リンク
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