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Федеральное агентство по образованию

Государственное образовательное учреждение высшего профессионального образования

ВОЛГОГРАДСКИЙ ГОСУДАРСТВЕННЫЙ ТЕХНИЧЕСКИЙ УНИВЕРСИТЕТ

(ВолгГТУ)

Кафедра иностранных языков

Семестровая работа за 9 семестр

по английскому языку

Тема: «Веб - сервисы»

Источник: http://www.msdn.com

Выполнил: студент группы САПР 5-2

Шиловский О. А.

Проверил: преподаватель

Чубарова И.С.

Краткая рецензия: …………………………………………………………………………

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

Оценка работы _________________ баллов

Волгоград 2004г.

Introduction to Web Services

No doubt you’ve been hearing a lot about Web Services lately. All the vendors and analysts are talking about them. Web Services are the next “new” thing.

The web services concept being championed by computing giants like Sun, Oracle, HP, Microsoft, and IBM doesn’t contain many new ideas, but it is a great step towards simple access to software over the network. By promoting standards–based communication, web services might change the way we build websites.

Sometimes the hype makes it seem as if Web Services will cure cancer and stop world hunger. It may seem like a lot of hype, but to some degree the hype is justified. Perhaps Web Services won’t rid the world of terrorism, but this new style of computing can improve your business. Web Services allow you to access and assemble the specific information and business processes that you need to accomplish your immediate business objective. Systinet calls this effect the Dynamic Enterprise.

A dynamic enterprise is an enterprise that can respond quickly to changing business conditions. As we find ourselves reeling from recent economic and political events, businesses need to find ways to reduce costs and improve efficiency; to streamline their business processes; to adapt their product mix; to establish new partnerships; to work more closely with customers. Web Services can help your IT department facilitate these changes rather than get in the way. Web Services enable the Dynamic Enterprise.

The basics principles behind web services are stunningly simple, and are nothing new in the world of distributed computing and the Internet: the web service provider defines a format for requests for its service and the response the service will generate a computer makes a request for the web services across the network the web service performs some action, and sends the response back.

Standards support

The reason that we should be suddenly interested in the services model is the incorporation of standard, open protocols for calling services and transmitting data.

While in the past many data and service providers have had proprietary standards or rough–and–ready data formats, we can now rely on simple eXtensible Markup Language (XML) based access over plain old HTTP. This means easier access and should let developers working with all sorts of technologies start playing the web services game.

The difference between web services and technologies developers have used in the past like DCOM, named pipes, and RMI, is that most web services rely on open standards, are relatively easy to command, and have widespread support across the Unix / Windows divide.

The Simple Object Access Protocol (SOAP) is a W3C standard protocol that defines the format for web service requests.

SOAP messages are sent back and forth between the service provider and service user in SOAP envelopes, containing a request for some action and the result of that action. SOAP envelopes are XML formatted, and are easy enough to decode.

Web Services are “plug and play” applications. A Web Service represents a piece of information or business process that can be accessed by anyone, anywhere, using any type of device. Web Services can be assembled and reassembled as needed to support the needs of the business.

Web Services represent the between the service-oriented architecture (SOA) and the Web. SOA has evolved over the last 10 years to support high performance, scalability, reliability, and availability. To achieve the best performance, applications are designed as services that run on a cluster of centralized application servers. A service is an application that can be accessed through a programmable interface. Clients access these services using a tightly coupled distributed computing protocol, such as DCOM, CORBA, or RMI. While these protocols are very effective for building a specific application, they limit the flexibility of the system. The tight coupling used in this architecture limits the reusability of individual services. Each of the protocols is constrained by dependencies on vendor implementations, platforms, languages, or data encoding schemes that severely limit interoperability. And none of these protocols operates effectively over the Web.

The Web Services architecture takes all the best features of the service-oriented architecture and combines it with the Web. The Web supports universal communication using loosely coupled connections. Web protocols are completely vendor-, platform-, and language-independent. The resulting effect is an architecture that eliminates(устраняет) the usual constraints of DCOM, CORBA, or RMI. Web Services support Web-based access, easy integration, and service reusability. A Web Service is an application or information resource that can be accessed using standard Web protocols. Any type of application can be offered as a Web service. For example, a Web service might provide:

• Stock quotes

• Weather reports

• Credit authorization

• Materials procurement

Web Services are applicable to any type of Web environment: Internet, intranet, or extranet. Web Services can support business-to-consumer, business-to-business, department-to-department, or peer-to-peer interactions. A Web Service consumer can be a human user accessing the service through a desktop or wireless browser, it can be an application program, or it can be another Web Service.

Emerging|появление| Web Services Technologies

Web Services can be developed using any programming language and can be deployed on any platform. Web Services can communicate because they all speak the same language: the Extensible Markup Language (XML). Web Services use XML to describe their interfaces and to encode their messages. XML-based Web Services communicate over standard Web protocols using XML interfaces and XML messages, which any application can interpret.

But XML by itself does not ensure effortless communication. The applications need standard formats and protocols that allow them to properly interpret the XML. Hence three new XML-based technologies are emerging as the de facto standards for Web Services:

▬ Simple Object Access Protocol (SOAP) defines a standard communications protocol for Web Services.

▬ Web Services Description Language (WSDL) defines a standard mechanism to describe a Web Service.

▬ Universal Description, Discovery and Integration (UDDI) provides a standard mechanism to register and discover Web Services.

Figure 1 shows how these technologies relate to one another. When a service provider wants to make the service available to service consumers, he describes the service using WSDL and registers the service in a UDDI registry. The UDDI registry will then maintain pointers to the WSDL description and to the service. When a service consumer wants to use a service, he queries the UDDI registry to find a service that matches his needs and obtains the WSDL description of the service, as well as the access point of the service. The service consumer uses the WSDL description to construct a SOAP message with which to communicate with the service.

Figure 1

SOAP

It seems like just yesterday SOAP wasn't more than a cleaning product. Now most developers can't hear the word without seeing angle brackets. SOAP originally stood for "Simple Object Access Protocol". If you had asked anyone what SOAP meant several years ago, they would have probably said something like "it's for making DCOM and Corba (e.g., RPC calls) work over the Internet". The original authors admit they were focused on "accessing objects" back then, but over time it became desirable for SOAP to serve a much broader audience. Hence, the focus of the specification quickly moved away from objects towards a generalized XML messaging framework.

The shift in focus creates a slight problem with the "O" in the SOAP acronym. Interestingly, the SOAP 1.2 Working Group has (so far) kept the SOAP name (it's so popular, how could they not?) but decided against spelling it out to avoid misleading developers. Today's official definition, found in the most recent SOAP 1.2 specification, doesn't even mention objects: SOAP is a lightweight protocol intended for exchanging structured information in a decentralized, distributed

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