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May 21, 2002—In this issue:
1. DEVELOPER .NET PERSPECTIVES
- What Is a Web Service?
- Attend Our Free Windows Security Solutions Webinar!
- Raising Windows 2000 Availability—Free Webinar
3. NEW AND IMPROVED
- Learn More About C# and .NET
4. CONTACT US
- See this section for a list of ways to contact us.
1. DEVELOPER .NET PERSPECTIVES
By now, you've probably heard of Microsoft .NET Framework's support for XML Web services, but you might not know what Web services are. A Web service is a Web site that doesn't have a UI because the Web service designed for programmatic access. Any security measure you can implement on a Web site you can duplicate in a Web service. In other words, the entire HTTP access model will work.
You might argue that some remote procedure call (RPC) implementations of distributed interfaces are Web services. Although these implementations are based on RPC and might use the Simple Object Access Protocol (SOAP) to support data interchange, I don't consider these RPC implementations to be Web services. A Web service is more than just a business object with a network interface. In particular, a Web service supports two evolving industry standards, the first of which is the Universal Description, Discovery, and Integration (UDDI) standard. One of the UDDI standard's primary goals is to support interoperable services that applications can discover and call from any client. As the "UDDI Executive White Paper" explains, you use an HTTP connection to access UDDI and discover existing Web services that meet your business needs. The second standard, the Web Services Description Language (WSDL), is under the control of the World Wide Web Consortium (W3C). As the WSDL standard notes, you can publish a WSDL file that lists any set of interfaces, including a file that lists only RPC interfaces. However, in theory, you can also publish a WSDL file that lists only COM interfaces. No matter whether you're using RPC or COM, publishing a WSDL file doesn't make that object's programmatic interface a Web service. I'm not saying that a service interface can't support COM, RPC, or both. As I'll discuss next week, good reasons exist for having a service support COM- or RPC-like interface.
Thus, to meet my definition of a Web service, the implementation needs to support an HTTP interface in addition to supporting elements such as UDDI and WSDL. The Web services' ability to support HTTP interfaces is a big deal because of the promise of interoperability. For years, you could use a variety of interfaces, including the distributed, Distributed COM (DCOM), Common Object Request Broker Architecture (CORBA), and Remote Method Invocation (RMI) interfaces. Although these interfaces support programmatic access, none of them act as a Web site. That distinction makes a difference when you need to use those interfaces. In the past, regardless of the interface you used, you likely experienced problems with accessing ports through a firewall or managing different protocols. For example, you couldn't call an RMI interface from Microsoft Visual Basic (VB) unless you had third-party software to reinterpret the call and reformat the data. With the .NET Framework, however, you can implement a Web service in Java that supports HTTP, then call that Web service from VB code without a third-party tool.
Writing Web services with Microsoft Visual Studio .NET is easy—and writing applications to use those services is even easier. In the same manner that you add a reference to a component or another .NET assembly in Visual Studio .NET, you can add a Web reference for a Web service. Web references let your GUI desktop application reach across port 80 and retrieve data, just like a user's browser. Your firewall problems go away, and you can use HTTP over Secure Sockets Layer (HTTPS) or another form of encryption to transmit data back and forth to a server anywhere in the world. You get all the power of a traditional Windows GUI and all the built-in logic and client processing that make Windows applications popular. And you can still obtain data from remote servers, no matter whether those machines are database servers or application servers that contain business logic written in COBOL.
With the .NET Framework, you can go beyond putting a front-end Web service on non-Windows system to display data for enterprise clients. Instead, you can create a GUI application that communicates with the non-Windows system and lets clients truly interact with that system's data. Hence, the Web services' glory doesn't lie in the ability to open a Web page that displays data in a browser. (Visual Studio .NET provides this ability for free.) Rather, the Web services' glory lies in the ability to let a native 32-bit Windows, Macintosh, or UNIX workstation application communicate with the same back-end Web service.
With Web services, you can overcome Web architecture problems, especially when you need to deal with interoperability. However, using a Web service isn't always the best solution. I'll discuss this topic next week.
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3. NEW AND IMPROVED
(contributed by Carolyn Mascarenas, [email protected])
O'Reilly announced "C# in a Nutshell" by Peter Drayton, Ben Albahari, and Ted Neward, a desktop reference for C# programmers. Each chapter in the API reference features an overview of a Microsoft .NET namespace and a quick reference entry for each type, including name, assembly category, description, member availability, and class hierarchy. The reference section also includes an accelerated introduction to the C# language and the .NET Common Language Runtime (CLR). Chapter 1, "Introducing C# and the .NET Framework," is free online. The reference costs $39.95. Contact O'Reilly at 707-827-7000 or 800-998-9938.
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