Introduction to XML

A "new" way to think about text

• structure not formatting
• portable representation
• enhanced content
• Details
• Markup in plain ASCII
• ISO 8879:1986
• 332 definitions; 70 basic
• history: GML
• DTD, Entity, Element

History

• Specific Coding (format-17)
• late 1960's: Generic Coding (header)
• 1969: GML (IBM, Goldfarb, Mosher, Lorie) - law offices
• Invented 1974 by Charles F. Goldfarb
• 1978: ANSI committee
• 1983: GCA standard
• 1985: final ISO 8879 draft
• 1987: DoD CALS
• 1993: ISO/IEC 10646 (instantiation of Unicode)
• 1994: RFC 1738: Uniform Resource Locators.
• 1996: XML Working Group formed

Acronyms

• SGML - Standard Generalized Markup Language
• DSSSL - Document Style Semantics Specification Lang.
• DTD - Document Type Description
• CALS - Computer-aided Acquisition + Logistic Support
• ISO - is *not* an acronym
• XML - eXtensible Markup Language
• XSL - eXtensible Stylesheet Language
• CSS - Cascading Style Sheets
• OASIS - Organization for the Advancement of
  Structured Information Standards
• ECMA - European Computer Manufacturers Assoc.

The design goals for XML are...

• ... shall be straightforwardly usable over the Internet.
• ... shall support a wide variety of applications.
• ... shall be compatible with SGML.
• It shall be easy to write programs which process [docs]
• The number of optional features in XML is to be kept
  to the absolute minimum, ideally zero.
• [docs] should be human-legible and reasonably clear.
• The XML design should be prepared quickly.
• The design of XML shall be formal and concise.
• XML documents shall be easy to create.
• Terseness in XML markup is of minimal importance.

What you can do with it

• smart editing
• automatic generation
• databases
• typed searching
• output processing
• easy parsing
  <tag> </tag>
  <tag attr=value>
  &lt; &amp; &gt;
  <emptytag/>
  &#38;

xml-lecture.sgml

<?XML version="1.0"?>
<!DOCTYPE slideshow SYSTEM "xslides.dtd">
<slideshow>
<title>Introduction to XML</title>
<author>Mark Eichin, SIPB</author>
<date>IAP 1999</date>
<slide>
<header>A "new" way to think about text</header>
<bullet>structure not content</bullet>
</slide>

slides.dtd

<!ENTITY lt "&#60;">
<!ENTITY gt "&#62;">
<!ENTITY amp "&#38;">
<!ELEMENT slideshow (title?, author?, date?, slide*)>
<!ELEMENT (header|title|author|date) (#PCDATA)>
<!ELEMENT slide (header, (bullet|subbullet|url|raw|example)+)>
<!ELEMENT bullet (#PCDATA)>
<!ELEMENT subbullet (#PCDATA)>
<!ELEMENT url (#PCDATA)>
<!ELEMENT raw (#PCDATA)>
<!ELEMENT example (#PCDATA)>

XML::Parser

• perl interface to add code to tags
  sub handle_start {
  my ($expat, $elem) = @_;
  ... } elsif ($elem =~ /^slide$/) {
  &inittag;
  print "%%Page: $pageno\n";
  print "($savetitle) showtitle\n";
  print "($pageno) showpageno\n"; $pageno++; } ...
  }
  sub handle_end {
  my ($expat, $elem) = @_;
  ... } elsif ($elem =~ /^slide$/) {
  print "finishpage\n";
  } ...
  $parser = new XML::Parser(Handlers => {
  Start => \&handle_start,
  End => \&handle_end });

HTML

Implementations

• SAX - Simple API for XML
• DOM - Document Object Model
• ESIS - Element Structure Information Set
• SX - SGML to XML normalizer
• IBM Alphaworks XML - Java
• XP - James Clark, Java
• LT XML (Edinburgh) - C
• XMLTok (was Expat) - C
• XMLParser class, xmlproc (Python)
• XML::Parser (O'Reilly, ActiveState)

More Implementations

• TclXML, TclExpat, ExCost
• MSXML - Java, C++
• sgrep - structured search
• Microsoft Internet Explorer 5beta
• AXSL - Activated XSL, Java Lobby site

Applications

• XBEL - XML Bookmark Exchange Language (Python)
• Microsoft CDF (Channel Definition Format)
• MicroSoft XML Notepad
• Web Spiders/Robots
• Digital Receipt Consortium DTD
• Mediacenter News Markup Language
• Oracle PLSXML - PL/SQL-based XML utilities
• DrawML
• XQL - XML Query Language
• MARC - MAchine Readable Cataloging

Docbook

Style Sheets

• DSSSL
  R4RS Scheme
  Document Style Semantics Specification Language
  ISO/IEC 10179:1996
• XSL
  ECMAscript (JavaScript) ECMA-262 extension
• Implementations
  XSLJ - convert XSL to DSSSL
  XT - James Clark Tree Constructor (Java)

Books

Other Stuff

• XLL XLink/XPointer
• Namespaces
• VRML moving to XML
• Languages
  Chinese
  Japanese
  French

Pointers