Introduction to XML Web Services

XML Web services are designed for interoperability with clients and other web services running on many different platforms. To accomplish this goal, XML Web services have been built using underlying technologies that are widely accepted standards in the computing industry. As you work with XML Web services, you will see references to the features of these underlying technologies over and over again. Here is a brief description of each of these important technologies that XML Web services are built on:

Hypertext Transfer Protocol  Hypertext Transfer Protocol (HTTP) is an application-level protocol by which text and other types of data can be transferred over the Internet. HTTP is supported on all platforms. HTTP traffic is usually allowed to move through corporate firewalls with little interference on well-known port 80. These factors make it a good choice for XML Web services, because no special access or proprietary formats need to be in place in order to communicate with clients and other web services.

Extensible Markup Language  Extensible Markup Language (XML) is a markup language that enables you to add tags and attributes to a data file; these tags and attributes serve to describe the meaning and structure of the data items. Although individual applications might use any tag names and organization of data they find appropriate, XML defines a few simple rules that ensure consistency among all XML documents. These rules include case-sensitivity, a uniquely named root element that encloses all the data, strict matching of start and end tags, proper nesting of elements within the hierarchy, and a few others. XML documents that are in compliance with all these rules are said to be 'well-formed.' A well-formed XML document can be processed by any standard software tool that can parse XML markup.

XML Schema Definition  XML Schema Definition (also referred to as XSD Schema) is a standard way to define an exact format for a specific XML document. Flexibility of the XML format is useful in some situations. However, when exchanging information between applications, the ability to validate against a specific XML format is important in ensuring data integrity and avoiding processing errors.

Simple Object Access Protocol  Simple Object Access Protocol (SOAP) is a standardized XML format that is used to exchange method calls and associated data between web services clients and servers. The SOAP protocol defines a set of XML tag names that form an 'envelope' for your message. Header tag names are defined for routing information. The Body section contains information about the method call, parameters, and return values. The Fault section contains error information on return from a method call, if a method call does not complete.

Universal Description, Discovery, and Integration  Universal Description, Discovery, and Integration (UDDI) is a service for locating XML Web services by consulting online registries, such as uddi.microsoft.com, which contain information about available web services. You can publish information about web services that your organization wants to make available, including the information or functionality that the service offers, contact information for support, technical details of your service, and more. If you are looking for a particular service, you can manually search the UDDI registry sites. There is a programmatic application programming interface (API) to access a UDDI registry server from your application. For example, if the server that you usually connect to is down, your application can search the registry at runtime, find another server that offers the same service, and connect to that one instead.

Note 

UDDI is discussed in more detail in Chapter 11, 'Deploying, Securing, and Configuring XML Web Services.'

In the .NET Framework, XML Web services are implemented as ASP.NET applications that run with Microsoft Internet Information Server (IIS). XML Web service files are indicated by an .asmx file extension. XML Web services use attributes to identify that classes and methods should be exposed to clients as a part of the XML Web service interface. Additionally, XML Web service classes must inherit from System.Web.Services.WebService, and your project must reference System.Web.Services.dll. After you have created your source code in Visual Studio .NET, you will compile your code into a DLL. This is the file that must be deployed to a web server and will handle all incoming requests for the service.



MCAD/MCSD(c) Visual Basic. NET XML Web Services and Server Components Study Guide
MCAD/MCSD: Visual Basic .NET XML Web Services and Server Components Study Guide
ISBN: 0782141935
EAN: 2147483647
Year: 2005
Pages: 153

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