What exactly is a Web service and under What circumstances should you use a Web service: Consider the current application development program, you will find an absolute inclination: people begin to prefer browser-basedclient application. This is certainly not because the client is able to provide a better user interface, but because it avoids spending on desktop applicationsthe high cost of publishing. Publishing Desktop ApplicationsThe cost is high, in half because of problems with application installation and configuration, and the other half because of the communication between the client and the server. Traditional Windows client applications use DCOM to communicate with the server and invoke remote objects. Configuring DCOM to work properly in a large network is a challenging task and a nightmare for many it engineers as well. In fact, many it engineers prefer to tolerate the limitations of the browser's functionality, rather than running a DCOM on the LAN. in my opinion, the result is an application that is easy to publish, but very difficult to develop and extremely limited in user interface. In extreme terms, you spend more money and time, but you develop applications that are weaker from the user's perspective. Don't believe me? Ask your accountant what the idea of the new browser-based accounting software is: The vast majority of business program users want to use a more user-friendly Windows UI. a perfect solution to the client-server communication problem is to use the HTTP protocol to communicate. This is because any machine running a Web browser is using the HTTP protocol. At the same time, many firewalls are currently configured to allow only HTTP connections. Many commercial applications also face another problem: interoperability with other programs. If all applications are written in the COM or. NET language and run on the Windows platform, it will be all right. In fact, however, most business data is still stored as non-relational files (VSAM) on large hosts and accessed by mainframe programs written in COBOL. Also, many commercial programs continue to be written in C + +, Java, Visual Basic, and a variety of other languages. In addition to the simplest programs, all applications need to integrate with and exchange data with applications running on other heterogeneous platforms. Such tasks are usually done by special methods such as file transfer and parsing, Message Queuing, and APIs that are only applicable in certain situations, such as IBM's Advanced Program-to-Program communication (APPC). Previously, there was no application communication standard, which was independent of the platform, the build model, and the programming language. Only through web Service, the client and the server are free to communicate with HTTP, regardless of the platform and programming language of the two programs.
we have at least two kinds of answers to this question. On the surface, a Web service is an application that exposes an API that can be called through the web. This means that you can programmatically invoke the application via the Web. We call the application calling this Web service a customer. For example, you want to create a Web service that is useful for returning the current weather conditions. Then you can create an ASP page that accepts the ZIP code as a query string, and then returns a comma-separated string containing the current temperature and weather. To invoke this ASP page, the client needs to send an HTTP GET. , and then returns a response. This ASP page should be counted as a Web service. It exposes an API that can be called through the Web because it is based on an HTTP GET request. The following is a more precise explanation of Web service: Web Services is to build interoperable, distributed applications's new platform. As a Windows programmer, you may have built a component-based distributed application with COM or DCOM. COM is a very good component technology, but we can easily cite the case that COM does not meet the requirements. The Web service platform is a set of standards that defines how applications can interoperate on the Web. You can write Web services on any platform you like, in any language you like, as long as we can query and access them through the Web service standard.
New Platform
The WEB service platform requires a set of protocols for the creation of distributed Applications . The WEB service platform must provide a standard set of type systems for communicating different types of systems in different platforms, programming languages, and component platforms. in traditional distributed systems, the interface-based (interface) platform provides methods for describing interfaces, methods, and parameters (such as IDL languages in COM and Cobar). Similarly, the Web service platform must provide a standard for describing Web service, allowing customers to get enough information to invoke the WebService. Finally, we must also have a way to make remote calls to this Web service. This approach is actually a remote procedure call Protocol (RPC). To achieve interoperability, this RPC protocol must also be independent of the platform and programming language.
technologies that make up the Web service platform:
XML and XSD
Extensible Markup Language (XML) is the basic format for representing data in a Web service platform. In addition to being easy to establish and easy to analyze, the main advantage of XML is that it is platform-independent and vendor-independent.
independence is more important than technical superiority.: Software vendors do not choose a technology that is invented by competitors.
XML solves the problem of data representation, but it does not define a set of standard data types, not to mention how to extend this set of data types. For example, what does shaping number mean? 16-bit, 32-bit, or 64-bit? These details are important to achieving interoperability. The
XML Schema (XSD) developed by the consortium is a set of standards specifically designed to address this problem. It defines a standard set of data types and gives a language to extend this set of data types.
the WEB service platform uses XSD as its data type system. when you use a language (such as VB. NET or C #) to construct a Web service, all data types you use must be converted to the XSD type in order to conform to the Web service standard. The tool you used may have automatically helped you with the conversion, but you will probably have to modify the conversion process to suit your needs.
SOAP When the Web service is built, you or someone else will call it.
The Simple Object Access Protocol (SOAP) provides a standard RPC method to invoke a Web service. In fact, soap is a bit of a misnomer here: it means that the following Web service is represented as an object, but that's not necessarily true: you can write your Web service as a series of C functions and still call it using SOAP. The SOAP specification defines the format of the SOAP message and how to use SOAP through the HTTP protocol.
Soap is also based on XML and XSD, and XML is the data encoding method of soap.
WSDLHow would you describe to others what your Web service does, and what parameters are available for each function call? You may write a set of documents yourself, and you may even verbally tell people who need to use your Web service. These informal approaches have at least one serious problem: when programmers sit in front of a computer and want to use your Web service, their tools, such as visual Studio, can't help them because they don't know your Web service at all. The
solution is to provide a formal description document in a way that the machine can read.
the Web Service Description Language (WSDL) is an XML-based language that describes Web service and its functions, parameters, and return values. WSDL is both machine readable and human readable, which is a great benefit. some of the latest development tools can generate WSDL documents based on your Web service, import WSDL documents, and generate code that invokes the corresponding Web service.
UDDI (Universal Description, Discovery and integration)a plan, based on standard service description and discovery specifications, to accelerate Web service rollout and enhance interoperability of Web services. The UDDI Business Registry is operated as a Web service by multiple actors in a resource-sharing manner. the core component of the UDDI plan is the UDDI business registration, which uses XML documents to describe the enterprise and the Web Service it provides. UDDI Business Registration provides three types of information:The white page contains the address, contact method, and known enterprise identity. Yellow page contains industry categories based on the standard taxonomy. Green page contains technical information about the Web service provided by the enterprise in the form of pointers to files or URLs that serve the service discovery mechanism.
suitable for use in Web service scenarios: 1. across Firewalls;2.application integration;3.Business-to-business integration;4.Software Reuse
scenarios where Web services are not suitable for use: 1. Standalone Application;2. Lanhomogeneous applications on the
which companies support WebService:Operating system is inseparable from the rich application of technology support. Similarly, the technology of WEB service can only reflect its value through an increasingly wide range of applications,
the most popular way to achieve this is to use. NET and Java two technologies, and the two implementation methods can be used to manipulate each other;Today we can see Web Service applications built using Web service building tools from different vendors such as Microsoft, Oracle, SUN, and Borland.
Microsoft. NET
Microsoft's. NET technology should be regarded as the most popular web Service development technology nowadays. First, because its company in the previous corresponding products occupy a considerable market share, so that the new launch. NET to have a relatively stable user base, and secondly, more importantly. NET platform not only continues theMicrosoftConsistent programming style, but also adds a lot of key technologies that support Web services, making it. NET has achieved a very good combination in the simplicity of operation and the stability of execution.Microsoftof visual Studio. NET is a convenient development tool for WEB services.MicrosoftThe goal is to--c# its new programming language as the preferred language for Web service. While C # looks like Java, there are some unique features that are not in Java. NET technology, the main tool for Web Service development is ASP. NET. Technically speaking, ASP. NET provides some advantages over previous versions of ASP (for example: separation of code and HTML, comparison with scripting languages, support for "real" programming languages such as C #).
IBM's WebSphere
IBM is the first company in the industry to offer an e-commerce infrastructure that fully supports Web services. Through years of joint efforts with the world Wide Web Consortium,
all IBM software, including DB2, Lotus, Tivoli, and WebSphere, provides comprehensive support for open technologies and standards such as SOAP, WSDL, UDDI, Linux, XML, and Java EE. IBM's WebSphere is also a better infrastructure software development platform. The WebSphere software platform and development tools include the WebSphere Studio application Developerwsad open standards based on Java EE, XML, and Web services, with IBM's key advantages in reliability, scalability, and security. WebSphere is the core platform of IBM's Web services strategy, supporting all the open standards and technologies necessary to develop, publish, and deploy Web services applications, including UDDI,SOAP,J2EE,WSDL, and enhancements to XML technology integration, This makes it a lot of users around the world.
Borland's JBuilderBorland company in JBuilder7, users can develop Web service and wireless applications more quickly with their Borland web Services Kit for Java and Borland JBuilder Mobileset 3. This will enable developers to easily create and integrate Web Service in the same development environment. The new JBuidler8 provides a convenient and efficient way to develop Web service. In summary, both. NET and Java are good choices for Web service development, and although there are some areas that need to be perfected, they are the best development tools and techniques. The specific choice of which development tools, but also the question of the benevolent see. Fundamentally, these two methods are not the best of the question, but based on the user's mastery of the two methods and the degree of preference for specific language to decide.
Web Service Learning Summary
