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<!DOCTYPE HTML PUBLIC "html.dtd"><HTML><HEAD><TITLE>Presenting XML:Automating the Web: Rapid Integration with XML:EarthWeb Inc.-</TITLE><META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW"><SCRIPT><!--function displayWindow(url, width, height) { var Win = window.open(url,"displayWindow",'width=' + width +',height=' + height + ',resizable=1,scrollbars=yes');}//--></SCRIPT></HEAD><BODY BGCOLOR="#FFFFFF" VLINK="#DD0000" TEXT="#000000" LINK="#DD0000" ALINK="#FF0000"><TD WIDTH="540" VALIGN="TOP"><!-- <CENTER><TABLE><TR><TD><FORM METHOD="GET" ACTION="http://search.itknowledge.com/excite/cgi-bin/AT-foldocsearch.cgi"><INPUT NAME="search" SIZE="20" VALUE=""><BR><CENTER><INPUT NAME="searchButton" TYPE="submit" VALUE="Glossary Search"></CENTER><INPUT NAME="source" TYPE="hidden" VALUE="local" CHECKED> <INPUT NAME="bltext" TYPE="hidden" VALUE="Back to Search"><INPUT NAME="sp" TYPE="hidden" VALUE="sp"></FORM></TD><TD><IMG SRC="http://www.itknowledge.com/images/dotclear.gif" WIDTH="15" HEIGHT="1"></TD><TD><FORM METHOD="POST" ACTION="http://search.itknowledge.com/excite/cgi-bin/AT-subscriptionsearch.cgi"><INPUT NAME="search" SIZE="20" VALUE=""><BR><CENTER><INPUT NAME="searchButton" TYPE="submit" VALUE=" Book Search "></CENTER><INPUT NAME="source" TYPE="hidden" VALUE="local" CHECKED> <INPUT NAME="backlink" TYPE="hidden" VALUE="http://search.itknowledge.com:80/excite/AT-subscriptionquery.html"><INPUT NAME="bltext" TYPE="hidden" VALUE="Back to Search"><INPUT NAME="sp" TYPE="hidden" VALUE="sp"></FORM></TD></TR></TABLE></CENTER> --><!-- ISBN=1575213346 //--><!-- TITLE=Presenting XML//--><!-- AUTHOR=Richard Light//--><!-- PUBLISHER=Macmillan Computer Publishing//--><!-- IMPRINT=Sams//--><!-- CHAPTER=15 //--><!-- PAGES=0283-0300 //--><!-- UNASSIGNED1 //--><!-- UNASSIGNED2 //--><P><CENTER><A HREF="0290-0293.html">Previous</A> | <A HREF="../ewtoc.html">Table of Contents</A> | <A HREF="0298-0300.html">Next</A></CENTER></P><A NAME="PAGENUM-294"><P>Page 294</P></A><H4><A NAME="ch15_ 13">Conditions and Error handling</A></H4><P>A significant feature of WIDL is conditionprocessing. Web-hosted applications return errors in different document formats than those used to returnsuccessful data responses. When unexpected document formats are returned asthe result of a service request, object references return either null values ormeaningless data.</P><P>In the case of the stockQuote service, a symbol of`XXX' might return a document containing the message'invalid symbol'.</P><P>The following simple condition element can handle this situation elegantly:</P><!-- CODE SNIP //--><PRE><CONDITION TYPE='FAILURE' REFERENCE='doc.h1[0].value' VALUE='*invalid symbol*' REASONTEXT='invalid symbol' /></PRE><!-- END CODE SNIP //--><P>In other words, the condition element compares the value of an objectreference to a known error condition. If the condition is met, the service failswith a message of `invalid symbol'.</P><P>Success conditions are also established using this mechanism:</P><!-- CODE SNIP //--><PRE><CONDITION TYPE='SUCCESS' OBJECT='doc.h1[0].value' VALUE='price' /></PRE><!-- END CODE SNIP //--><P>In this case, the service can be considered successful only if the specifiedobject reference returns a value of `price', indicating that the expecteddocument has been returned.</P><P>Finally, conditions are used to divert a service to an alternate set of objectreferences for output variables. This functionality is required when a Webapplication returns different document structures based on submitted inputcriteria. Different SKU numbers, for instance, often refer to items that arepresented in pages with varying layouts.</P><H4><A NAME="ch15_ 14">XML Documents</A></H4><P>Interfaces to services returning data in XML formats are described inWIDL in the same manner as services returning HTML documents. The maindifferences are that object references are less obscure and less likely to beimpacted by major changes in document presentation, and that the process ofconstructing WIDL files is simplified by the presence of DTDs describing data schemas.</P><A NAME="PAGENUM-295"><P>Page 295</P></A><H3><A NAME="ch15_ 15">E-Commerce Extrapolations</A></H3><P>Many companies make the mistake of equating electronic datainterchange (EDI) with electronic commerce. EDI is a set of standards to facilitatebusiness-to-business ordering and fulfillment processes, whereas electroniccommerce embraces online querying of supplier databases and the real-timeintegration of supply chains over extranets and the Internet.</P><P>Electronic commerce, or e-commerce, in fact addresses a much broaderexchange of information that facilitates ordering and fulfillment processes. Bute-commerce on the Web is threatened by the proliferation of incompatible platformsthat introduce proprietary protocols for communications between buyersand suppliers. Vendors of such platforms attempt to leverage buyer andsupplier relationships to sell their solutions on both sides of the network. It's veryrare, however, for an organization to possess the clout to force all buyers orsuppliers to conform to one e-commerce infrastructure.</P><P>The many-to-many reality of buyer-supplier relationships mandates that acommon ground be found. When restricted to standard Web protocols,e-commerce systems today can provide only browser-based access totransactional systems.</P><P>In many ways, e-commerce confronts obstacles similar to thoseexperienced by middleware vendors attempting to integrate systems from differentbusiness units within the same organization. Crossing organizational boundarieswith middleware technologies often introduces political tensions becausesoftware components must be purchased, installed, and integrated with diversesystems on either side of a network. In most cases, such integration efforts can besuccessfully driven only by executive vision.</P><H4><A NAME="ch15_ 16">Middleware Without the Middle: Middleware for the Masses</A></H4><P>The use of XML metadata as an enabling mechanism forbusiness-to-business integration over standard Web protocols facilitates a move frommanually driven information links to automatic application links.<BR>XML metadata requires only that a system be Web-enabled in order for itto be integrated over standard Web protocols. Hundreds, if not thousands,of vendors offer products to Web-enable existing databases and legacysystems,</P><A NAME="PAGENUM-296"><P>Page 296</P></A><P>effectively removing the middleware dilemma. Because proprietarytechnologies are not required on both ends, there is in fact no middle. Buyers andsuppliers of all sizes can use the Web-enabling technology of their choice,leveraging any investments they might have already made.<BR><P>Flexible deployment is perhaps the most important attribute of anXML-based IDL for the Web. Instead of requiring all e-commerce_enabled sites toprovide WIDL for their services, WIDL files can be centrally orindependently managed by a buyer, a supplier, or a third party, or by a combination ofbuyer, supplier, and third party.<BR><P>The next step is a service-based view and brokerage of Web functionalitythat enables a new level of integration.</P><P>Consumer-focused agent technologies are already aggregating services suchas online ordering of books and CDs. CommerceNet, a consortium ofindustry and technology leaders promoting Internet-based commerce, envisionsan economy of online services and virtual markets linked via an open Webplatform that enables them to utilize and add value to each other's services.</P><P>An XML-based IDL such as WIDL provides the platform for astandards-based approach to the aggregation of functional services into verticalapplication domains, such as package tracking, healthcare, and financial services.</P><H4><A NAME="ch15_ 17">The Transformation of the Web</A></H4><P>Web servers were originally designed to feed HTML to browsers forhuman consumption. Because the Web has been almost exclusively designed forthe end-user, businesses have capitalized on Web technology to makebusiness systems accessible via Web browsers.</P><P>Today, businesses are moving aggressively to capitalize on the integrationof business systems made possible by intranet and Internet technologies.Although the Web infrastructure provides basic connectivity, it does not provide astandard integration platform. Web sites have been unable tointercommunicate without extensive hand-coding.</P><P>An open market requires support for many-to-many buyer-supplierconnections. Integration via proprietary technologies threatens to limit thenumber of connections and therefore the openness of markets. Vendors, especiallysmall vendors, cannot afford to maintain multiple proprietary technologies,which only increase complexity and exacerbate problems in management ofinformation systems.</P><A NAME="PAGENUM-297"><P>Page 297</P></A><P>XML metadata in the form of an Interface Definition Language for theWeb can deliver a practical and secure mechanism for the integration ofbusiness systems over standard Web protocols.</P><H3><A NAME="ch15_ 18">Summary</A></H3><P>The World Wide Web is providing millions of end-users withaccess to ever-increasing volumes of information. Although the Web initially servedstatic documents to browsers, dynamic content has rapidly emerged to provideend-users with interactive information services including package tracking,travel reservations, and online purchasing.</P><P>On corporate intranets and extranets, the Web browser has enabledaccess to business systems, but in many cases it has reinforced manualinefficiencies because data must be transcribed from browser windows into otherapplication interfaces. Understandably, the technology behind public contentsites and corporate applications has been focused almost exclusively on thepresentation of data. HTML extensions and hacks, which embed ancillaryinformation in proprietary tags or comments, are workarounds that have enableddynamic data to be merged with HTML templates for display purposes. Inevitably,data structure information is lost in the process.</P><P>Browser plug-ins and applets have extended browser functionality, butthey have introduced numerous proprietary message and document formats. Ina world of many-to-many relationships, a standard forcross-organizational messaging and data transfer is sorely needed.</P><P>XML will address all of these concerns. XML preserves data structureinformation and provides a standard message format. Furthermore, XML metadatais now being employed to define Web content for push channels, and there isan active project within the W3C to use XML syntax to define a far broaderstandardized, portable, metadata format for Web content. XML is poised totransform the Web.</P><P>This chapter has presented the view that XML metadata in the form ofan Interface Definition Language (IDL) also can be used to definefunctional interfaces to business objects on the Web.</P><P>Interactions normally performed manually in a browser—such asentering information into an HTML form, submitting the form, and retrievingHTML documents—can be automated by capturing details such as inputparameters,</P><P><CENTER><A HREF="0290-0293.html">Previous</A> | <A HREF="../ewtoc.html">Table of Contents</A> | <A HREF="0298-0300.html">Next</A></CENTER></P></TD></TR></TABLE></BODY></HTML>⌨️ 快捷键说明
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