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<!DOCTYPE HTML PUBLIC "html.dtd"><HTML><HEAD><TITLE>Presenting XML:Implementing 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=04 //--><!-- PAGES=0051-0066 //--><!-- UNASSIGNED1 //--><!-- UNASSIGNED2 //--><P><CENTER><A HREF="0055-0059.html">Previous</A> | <A HREF="../ewtoc.html">Table of Contents</A> | <A HREF="0064-0066.html">Next</A></CENTER></P><A NAME="PAGENUM-60"><P>Page 60</P></A><H4><A NAME="ch04_ 9">Converting to XML</A></H4><P>Up-conversion, as it is known, is usually a mixture of software processesand hard work. The software processes are concerned with finding clues inthe existing documents that can be mapped automatically to XML markup.This pattern matching can be based on the page layout of the source document,or the conversion software can provide a general-purpose language in whichyou write scripts to process specific source formats. The hard work can happenon either side of the software process.</P><P>A general problem is that current documents typically contain lessinformation than you want in your XML version. For example, italicized wordsand phrases within paragraphs might be italicized because they are</P><UL><LI> Foreign words<LI> Emphasizing a point<LI> Technical terms<LI> Representing irony</UL><P>You usually should distinguish these cases in your XML markup. So, evenif your conversion software is able to pick out these phrases in italics, youstill have some manual work to do. You can seed the document with clues tohelp the software before processing it. Or you can edit the document by handafter processing to improve the quality of markup.</P><P>Up-conversion is often an iterative process. It makes sense to convertdocuments to a low-level DTD, which does little more than mirror theiroriginal logic in a valid XML form. XML-aware software can then be used tosuccessively enhance the XML markup until it is acceptable.</P><P>The scale of an up-conversion project can be very large. If a corporation <BR>decides to re-engineer its internal documentation around XML, it mightwant to convert five years of material to this format. You easily might have tolook at tens of thousands of documents in an interesting variety of formats! Forthis reason, a number of firms earn a living by taking on data-conversionprojects. Many of these firms are already proficient in up-conversion to SGMLand would find XML no problem.</P><A NAME="PAGENUM-61"><P>Page 61</P></A><H4><A NAME="ch04_ 10">XML to XML Conversions</A></H4><P>When you have your documents in XML format, other types ofconversion jobs will crop up. These require a slightly different kind of softwarebecause you are now starting from a well-structured source.</P><P>One very common need is to convert from one XML-style format toanother. For example, you might want to convert documents from an in-houseXML DTD to HTML for easier delivery on the Web. Such a process istypically driven by a script that tells you what to do with each element type (convertit to another element type, ignore it, output its data content withoutsurrounding markup, and so on). Like a style sheet, the script is actually driven bythe document itself.</P><H4><A NAME="ch04_ 11">XML to Other Formats</A></H4><P>Finally comes the process known asdown-conversion, which entails moving from XML to non-XML form. This is actually the province of the XS stylemechanism, although other software also does this job. XS is clearly biased towarda paginated result. It specifies the required result in terms of things thatappear on the page, such as paragraphs. Then a back-endprocessor converts this generalized description to the actual format required—RTF, TeX, PostScript,and so on.</P><P>This book was authored in SGML and then down-converted to RTF so thatit could be fed into Sams Publishing's Word-based production process. I useda freeware package called Jade, by James Clark, which supports the subsetof DSSSL on which XS's design was based.</P><P>In some cases, you actually want an unpaginated output from your XML.For example, if you are outputting selected elements from an XML documentto be loaded into a database, you really want just a comma-delimited filecontaining only the required elements in the correct order. In this case, aspecialized XML-aware down-conversion program is probablyrequired.</P><A NAME="PAGENUM-62"><P>Page 62</P></A><H3><A NAME="ch04_ 12">Publishing</A></H3><P>Publishing from your XML documents can take a variety of forms. Inaddition to the obvious option of Web-based publishing (enhancing your Website with XML-based pages), the following possibilities spring to mind:</P><UL><LI> Print<LI> CD-ROM<LI> On-demand and custom publishing</UL><P>Let's start with Web delivery of your XML documents. I think it isreasonable to assume that future releases of standard Web browsers such as Netscapeand Internet Explorer will offer seamless integration of XML with theircurrent HTML capabilities. Assuming that this happens, you can develop yourWeb site with whatever mixture of HTML and XML makes sense for yourparticular circumstances, and you can be confident that your clients will havesoftware that can read all of your pages. On the server side, you simply haveto ensure that your XML documents are served with the correctMIME-type—text/xml. In addition, it is quite possible that specialized client-sidebrowsers will be developed for specific XML applications.</P><P>The built-in XS style mechanism offers a reasonable quality of printedoutput directly from your XML documents. Current DSSSL implementations(which support XS) offer a variety of back-end formats that can be fixed (TeX) orrevisable (Rich Text Format).</P><P>If you require higher-quality print products, your XML documents can befed to a typesetting/desktop publishing (DTP) program. You have two optionshere. In the first case, you must convert your XML documents to the inputformat required by your DTP package. This is an example of a down-conversion(as discussed in the previous section). Alternatively, if you have a DTPprogram that is XML-aware, all you need to do is load the document as it stands.This is obviously the better route. Apart from avoiding the conversion process,you also avoid the problem of having the same document in two revisableformats. This can (and usually does) lead to inconsistencies between the printeddocument and its XML source.</P><A NAME="PAGENUM-63"><P>Page 63</P></A><P>Producing a CD-ROM from XML documents leads to a requirement forsoftware that indexes and organizes a set of XML documents into anelectronic book. This software might be self-contained, holding the documents in aproprietary non-XML format, or it might simply set them up so they can be viewed bya standard XML browser application.</P><P>On-demand publishing and current awareness services require some sortof XML-aware search engine that can pick out the relevant material matchinga one-off query or a user profile. The selected documents (or parts ofdocuments) can then be delivered using standard Web publishingtechniques.</P><H3><A NAME="ch04_ 13">Site Maintenance</A></H3><P>Although it is quite feasible to manage a small hybrid XML/HTML Website by hand, this option becomes untenable at some point as the site grows. Ifthe Web site is actually a company-wide intranet, software support for itsmaintenance is usually a necessity.</P><P>Document management systems allow a whole mass of documents to bemanaged and served in a coherent manner. This includes operations such asthe following:</P><UL><LI> Storing all the documents in a single repository<LI> Enforcing appropriate access rights for each user<LI> Checking out complete and partial documents for editing<LI> Locking checked-out documents so that no one else can updatethem at the same time<LI> Logging changes to a document when it is checked in after editing<LI> Creating publications from a set of documents</UL><P>Ideally, an XML document management system takes account of boththe physical organization of your documents (into entities) and their logicalorganization (into elements). This gives you the best chance to manage yourinformation resources effectively, avoiding redundancy of information.Current experience from the SGML world suggests that a wide range of XMLdocument management systems will be available, offering dramatically diverse <BR>solutions to this problem.</P><P><CENTER><A HREF="0055-0059.html">Previous</A> | <A HREF="../ewtoc.html">Table of Contents</A> | <A HREF="0064-0066.html">Next</A></CENTER></P></TD></TR></TABLE></BODY></HTML>⌨️ 快捷键说明
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