可扩展性标记语言XML中英文资料外文翻译文献.docx

1、可扩展性标记语言XML中英文资料外文翻译文献可扩展性标记语言XML中英文资料外文翻译文献Understanding the Extensible Markup Language (XML) This appendix takes a look at the Extensible Markup Language (XML)a superb structured document format standard that businesses are using to exchange business data. XML complements EJB nicely as well; in fa

2、ct, the EJB 1.1 specification uses XML as a document format for deployment descriptors. By reading this appendix, you will learn the following: Why businesses need XML The core concepts behind XML programming How EJB and XML are related (which well expand upon in Appendix D, covering EJB 1.1) XML is

3、 an extremely important technology for the Internet, and it is destined to become the de-facto standard for structuring document content. If you already know XML, feel free to skip to the second half of this appendix, where we discuss how XML and EJB are related. Otherwise, read on, and we will expl

4、ain XML from the ground-up. This appendix explains enough XML for you to begin programming with EJB 1.1. For a full tour of XML, see the books accompanying Web site for links to external resources. Business Needs for XML We begin by studying the needs of the business community that make XML such a u

5、seful standard. Why is XML important? What business problems does it solve? Why did we need to create XML rather than use existing technology? Those are the questions we will answer in this section. Electronic Commerce The business need for a standard such as XML has arisen with the advent of electr

6、onic commerce (also called e-commerce, e-business, or your favorite buzzword). When most people hear the word “electronic commerce”, they usually think of Web storefronts that you can visit to purchase goods electronically. This is called business-to-consumer e-commerce because a business is conduct

7、ing a transaction with a consumer. Examples of business-to-consumer Web sites are A (), B (), and carO (www.carO). But e-commerce extends beyond simply the business-to-consumer model. For instance, an online auction house such as eBay () facilitates trans- actions between consumers by hosting auctio

8、ns. This is called consumer-to- consumer e-commerce because goods are exchanging hands between consumers. A business may also sell goods to other businesses and take consumers out of the picture altogether. This economic model is called business-to-business e-commerce, and is where most of the money

9、 changes hands by far, because every business needs to conduct inter-business transactions to survive. Manufacturers need to buy parts from suppliers. Resellers need to buy products from manufacturers. And all corporations need to buy office supplies and furniture. Geographically distributed compani

10、es, conglomerates and even whole industries (such as aerospace) rely on communication, and the ability to distribute manufacturing activities gives some companies an essential economic advantage. Business-to-business e-commerce is the single largest financial impact the Internet is making on the wor

11、ld economy, and has been estimated to be 20 times as large as the other Internet economic models. As we will see, business-to- business e-commerce is where XML has the largest impact as well. Inadequacies with Existing Technology The challenge for businesses to conduct affairs electronically is for

12、businesses to understand each others data, such as products, customers, and financial data. With a paper-based system, a human being always intervened and could make Go back to the first page for a quick link to buy this book online! logical guesses about ambiguous data. With electronic business, ho

13、wever, computer programs need to receive accurate, structured data, or millions of dollars could be lost due to incorrect transactions. Thus, a structured data document standard is needed that businesses can use to share information. This document standard should be simple enough for anyone to use e

14、legantly, yet be powerful enough to represent any business data. A computer program should be able to read an electronic document structured in this language and figure out the semantic details of the document based on its structure. For example, an application should be able to query a digital purc

15、hase order document and determine what product and quantity the purchase order is for. Lets take a look at the existing technology standards and examine why they are inadequate for our needs. VANs and EDI Electronic business is not a new concept. Companies have already been doing it for years in a v

16、ery proprietary way. Before the Internet hit mainstream, two corporations would conduct business electronically using a third-party vendors value-added network (VAN), or private network that links companies together. The largest four VAN vendors are General Electric Information Services, IBM Global

17、Information Network, Sterling Commerce, Inc., and Harbinger Corporation. The standard for conducting business over VANs is called Electronic Data Ex- change (EDI), a standard for facilitating the electronic exchange of data. EDI has traditionally been used over VANs although it is been extended to r

18、un over the Internet as well. EDI has widespread use in multiple vertical industries, from the business sector (transferring business documents) to the educational sector (transferring student records, transcripts, and test scores). The problems with VANs and EDI are as follows: VANs using EDI are a

19、 very expensive subscription service, and charge businesses outrageous per transaction fees. VANs are a challenge to link to other businesses that are already on the Internet. VANs are designed for batch-mode processing (rather than just-in-time processing, which is necessary for efficient transacti

20、ons). Within industries, large companies typically define a set of EDI templates that lock other companies into proprietary standards for data exchange. EDI is an outdated, cumbersome, and non-extensible format for transferring data. Note that there is definitely a lot to be said about VANs and EDI.

21、 Many businesses run quite smoothly on these technologies today, as VANs using EDI are quite reliable and secure. Many corporations are also very concerned about gambling their businesses on anything new. Due to these factors, plus the slow rate of technology adoption, the EDI market is growing rapi

22、dly as we speak. In the long run, though, VANs and EDI are likely to die off in favor of newer technology evolutions. What would you do to replace VANs and EDI with an Internet-based model? First you would need to replace the proprietary VAN networks with an Internet link. Thats simply a hardware pr

23、oblem. The larger issue is replacing or enhancing EDI with an efficient, modern, structured data document standard that business can use to exchange information. As we will see, XML is that standard, and it is what early adopting businesses are tackling as an integration method, even as we speak. SG

24、ML The Standard Generalized Markup Language (SGML) is a meta-markup languageyou can use a meta-markup language to design your own markup language (such as XML or HTML). SGML provides a mechanism to add structure to your documents, and has a great track record of successful deployments of application

25、s, especially in the publishing realm. But, unfortunately, SGML has never become mainstream, largely because of its complexity. SGML is quite powerful, and it could easily be used to represent business data. Its power comes at the cost of ease of use, as SGML is a bit too powerful for everyday busin

26、ess applications. The ramp-up curve for programming with SGML is particularly steep, and the high cost of leveraging SGML is very prohibitive. Few people use SGML in its raw form, but everyone uses implementations of SGML, such as HTML and XML. HTML The HyperText Markup Language (HTML) is the predom

27、inant standard for Web documents. HTML is an application of SGML that is intended for multimedia presentation of information over the Internet. HTML is an inappropriate markup language for electronic data, primarily because HTML was designed around the use of GUI tags, rather than business data cont

28、ent. HTML is great for displaying documents to end users, but it is very poor for defining other structure in a document. For example, consider the following HTML snippet: John Doe The Doe Corporation Here, The and tags tell the client-side browser to represent the associated text in bold and italic

29、s, respectively. However, the structure ends there. The browser has no way of structuring the semantic meaning of the text within the document. For example, by glancing at this code, theres no way we can automatically identify that the string “John Doe” is the name of a person. Nor can a computer pr

30、ogram discern that “The Doe Corporation” is the name of a company. Note that there are clunky ways around this (for example, you could add ID attributes). Similary, HTML is not extensible. If a business needs to add new tags to accommodate its needs, that business will run into a wall with HTML. Thi

31、s is because HTML is a markup language, but is not a meta-markup language. XML The Extensible Markup Language (XML) is a universal standard for structuring content in electronic documents. XML is extensible, enabling businesses to add new structure to their documents as needed. The XML standard does

32、 not suffer the version control problems of other markup languages such as HTML because it has no predefined tags. Rather, with XML you define your own tags for your business needs. XML is a meta-markup language because you can define your own markup language which is self-describing. This makes XML the ideal document format for transferring business data electronically, and it has a wide variety of other applications as well. Benefits of XML From a business perspective, XML is compelling because it allows businesses to structure data in an elegant, ex