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<!DOCTYPE HTML PUBLIC "html.dtd"><HTML><HEAD><TITLE>Presenting XML:Potential Applications of 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=18 //--><!-- PAGES=0331-0356 //--><!-- UNASSIGNED1 //--><!-- UNASSIGNED2 //--><P><CENTER><A HREF="0335-0337.html">Previous</A> | <A HREF="../ewtoc.html">Table of Contents</A> | <A HREF="0341-0343.html">Next</A></CENTER></P><A NAME="PAGENUM-338"><P>Page 338</P></A>entity references), Sun is trying to implement an external catalog thatwill describe the locations to which links can be resolved. Imagine you arereading a manual online and you click on a hyperlink to a different manual. Thiscatalog would be consulted and the manual you have asked for would belocated on your workstation. If it wasn't present locally, the software could bedirected to look on the local network for the manual. If the manual couldn't befound on the local network, the link resolution mechanism could ultimately bedirected all the way back to Sun's documentation server in MountainView, California, where a copy would always be found.</P><P>Taking this a few steps further, this link resolution mechanism will allowSun to accommodate some other intriguing situations:</P><UL><LI> When a book is moved to a different server, all the links to itstill work.<LI> When I'm reading in one language and a link takes me to amanual that isn't available in that language, I can automatically be switchedto another preferred language if that is available.<LI> If I want to have my documentation installed locally to haveit available as quickly as possible, I can still link to the very latestinformation on the Internet without necessarily even noticing thatI've moved offsite.</UL><P>The last word surely belongs to the team members themselves:</P><BLOCKQUOTE>"We are actively supporting the delivery of XML today and herecome the applications. Do you think that Microsoft and Netscape ownthe WWW market? Think again....XML is!" <BR><BR>Eduardo Gutentag and Jeff Suttor, from a paper presented at theSGML Europe '97 conference in Barcelona, Spain, May 1997.</BLOCKQUOTE><H4><A NAME="ch18_ 6">MathML</A></H4><P>The markup of mathematical formulae and equations has had a long andcomplicated involvement with electronic distribution. Long before the WorldWide Web was even dreamt of, scientists were accessing databases containingmathematics marked up in TeX.</P><A NAME="PAGENUM-339"><P>Page 339</P></A><P>Somehow, however, mathematics and HTML have never quite managedto live together. The extension of HTML has been "on the way" for so longthat even devotees have started to wonder whether it will ever happen.Proposals have been made, drafts have been circulated and discussed, and there waseven a WWW browser (called Athena, which was available for the UNIXoperating system only) that was able to interpret the HTML codes for basicmathematical equations. The syntax was rather simple, and the codes that it offeredwere a little limited, but given a little patience and some persistence, it wasquite feasible to be able to include basic equations, matrices, and integrals, evenif they did get a bit long for even relatively simple formulae, like this:</P><!-- CODE //--><PRE><MATH>{&int<SUP>a</SUP><SUB>b</SUB><LEFT>{f(x)<OVER>1-x} dx}<BR></MATH></PRE><!-- END CODE //--><P>The HTML codes for mathematics were present in the March 1995 draftof HTML 3.0. In the discussion documents for HTML 3.2 (code namedWilbur), they had vanished. In the January 1997 W3C Reference Specificationrecommendation for HTML 3.2 (code named Cougar), it is as if they had neverbeen there! Instead, in a small working draft called "additional named entities,"a set of mathematical symbol entities are proposed for characters that canbe represented as glyphs, as they appear in the Adobe Symbol font. Largesymbols such as brackets, braces, and integration signs can then be built out ofthese glyphs by using their numerical codes:</P><!-- CODE SNIP //--><PRE>&#189;&#913;&#178;</PRE><!-- END CODE SNIP //--><P>This is the code for the expression "one half alpha squared."</P><P>Strangely, the result is somewhat reminiscent of the printing codes thatyou used to have to insert into your text back in the 1960s to achieve a similar <BR>effect.</P><P>All is not lost, however, because it is here that XML is already beginningto prove the value of its extensibility. In April 1995, shortly after theWWW conference in Darmstadt, Germany, at which the proposal for HTMLMath was dropped, a group of interested parties formed to discuss the problemfurther. Over the following years, the informal group grew into a formalW3C working group, attracting members from such renowned sources as theAmerican Mathematical Society and Elsevier Science Publishers. Finally, inMay 1997, the group published a working draft of the specification of anXML application called the Mathematical Markup Language (MathML).</P><A NAME="PAGENUM-340"><P>Page 340</P></A><P>Of course, as with so much involved with XML, there is still a lot of groundto be covered and a lot more work to be completed, but the working groupalready has an agenda in mind. June, July, and August of 1997 will seethree planned revisions, with a formal recommendation being made inSeptember 1997, and a second working draft being made in May 1998. Beyond thatdate, only the group members can guess at what the timetable will be.</P><H4><A NAME="ch18_ 7">Presentation and Content</A></H4><P>MathML represents a very interesting variation on a theme that haspervaded the SGML world since the very beginning: the seemingly conflictinginterests of presentation-based and content-based markup.Presentation-based markup is primarily concerned with the appearance of the final result, and it hasgiven rise to such HTML elements as the horizontal line<HR> and <BLINK>. Content-based markup, on the other hand, is far more interested inidentifying the information content of a document so that interesting things can bedone with it, such as render it audibly for the sight-impaired, or even (in the caseof MathML) submit it to a computer algebra system that can plot or solvethe equation for you.</P><P>Perhaps recognizing that a picture really is worth a thousand words,MathML intends to incorporate both presentation-based and content-basedmarkup schemes. Consider the simple binomial equation ofx(x + 4) = 1. Multiplying out the brackets, this can be written using purely presentation codesas follows:</P><!-- CODE //--><PRE><MROW> <MROW> <MSUP> <MI>x</MI> <MN>2</MN> </MSUP> <MO>+</MO> <MROW> <MN>4</MN> <MO>&InvisibleTimes;</MO> <MI>x</MI> </MROW> <MO>-</MO> <MN>1</MN> </MROW> <MO>=</MO> <MN>0</MN></MROW></PRE><!-- END CODE //--><P>Here the codes merely describe the appearance of the symbols on the page.</P><P><CENTER><A HREF="0335-0337.html">Previous</A> | <A HREF="../ewtoc.html">Table of Contents</A> | <A HREF="0341-0343.html">Next</A></CENTER></P></TD></TR></TABLE></BODY></HTML>⌨️ 快捷键说明
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