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In understanding the mechanics of XML, we examined what markup is, the syntax of tags, and how start, end, and empty tags are used. We continued to explore the mechanics of XML by learning the difference between well-formed and valid documents, how we define the legal elements and attributes using XML Schema, how to use namespaces to create unique element and attribute names, and how applications and browsers represent documents internally using the Document Object Model. After understanding XML, we turned to its impact on the enterprise. XML has had considerable impact on 10 areas: data
Understanding XML and Its Impact on the Enterprise
exchange, ebusiness, EAI, IT architectures, CMS, knowledge management, portals, CRM, databases, and collaboration. XML's influence will increase dramatically over the next 10 years with the advent of the Semantic Web.
Lastly, we turned a critical eye on the current state of XML meta data and why it is not enough to fulfill the goals of the Semantic Web. The evolution of meta data will expand into three levels: modeling of things, modeling of knowledge about things, and, finally, modeling "closed worlds." In addition to modeling knowledge and worlds, we will expand to model the rules and axioms of logic in order for computers to automatically use and manipulate those worlds on our behalf. Finally, to apply those rules, standard inference engines, like CWM, will be created and embedded into many of the current IT applications.
In conclusion, XML is a strong foundation for the Semantic Web. Its next significant stage of development is the advent of Web services, discussed in the next chapter.
Understanding Web Services
"By 2005, the aggressive use of web services will drive a 30% increase in the efficiency of IT development projects."
"The Hype Is Right: Web Services Will Deliver Immediate Benefits," Gartner Inc, October 9, 2001.
Web services provide interoperability solutions, making application integration and transacting business easier. Because it is now obvious that monolithic, proprietary solutions are barriers to interoperability, industry has embraced open standards. One of these standards, XML, is supported by all major vendors. It forms the foundation for Web services, providing a needed framework for interoperability. The widespread support and adoption of Web services— in addition to the cost-saving advantages of Web services technology—make the technologies involved very important to understand. This chapter gives an overview of Web services and provides a look at the major standards, specifications, and implementation solutions currently available.
What Are Web Services?
Web services have been endlessly hyped but sometimes badly described. "A framework for creating services for the use over the World Wide Web" is a fairly nondescriptive definition, but nonetheless, we hear marketing briefs telling us this every day. The generality of the definition and mischaracteriza-tion of "Web" to mean World Wide Web instead of "Web technologies" makes this simple definition do more harm than good. For this reason, we will give a more concrete definition of Web services here, and then explain each part in detail.
Web services are software applications that can be discovered, described, and accessed based on XML and standard Web protocols over intranets, extranets, and the Internet. The beginning of that sentence, "Web services are software applications," conveys a main point: Web services are software applications available on the Web that perform specific functions. Next, we will look at the middle of the definition where we write that Web services can be "discovered, described, and accessed based on XML and standard Web protocols." Built on XML, a standard that is supported and accepted by thousands of vendors worldwide, Web services first focus on interoperability. XML is the syntax of messages, and Hypertext Transport Protocol (HTTP), the underlying protocol, is how applications send XML messages to Web services in order to communicate. Web services technologies, such as Universal Description, Discovery, and Integration (UDDI) and ebXML registries, allow applications to dynamically discover information about Web services—the "discovered" part of our definition. The message syntax for a Web service is described in WSDL, the Web Service Definition Language. When most technologists think of Web services, they think of SOAP, the "accessed" part of our Web services definition. SOAP, developed as the Simple Object Access Protocol, is the XML-based message protocol (or API) for communicating with Web services. SOAP is the underlying "plumbing" for Web services, because it is the protocol that everyone agrees with.
The last part of our definition mentions that Web services are available "over intranets, extranets, and the Internet." Not only can Web services be public, they can exist on an internal network for internal applications. Web services could be used between partnering organizations in a small B2B solution. It is important to understand that there are benefits for using Web services internally as well as externally.