CHAPTER 1 SGML/XML:

TERMS, DEFINITIONS,
AND INFORMATION

  MARKUP LANGUAGES

  Markup languages specify the insertion of markup tags into electronic
documents.

  In general, markup tags are structure and content tags, such as
<poemtitle>, but style tags are sometimes used too, such as HTML's
<B> bold-text tag.








  SGML
(STANDARD GENERALIZED MARKUP LANGUAGE)

  Not really a markup language, but rather a "metalanguage."
SGML is the international standard for creating markup languages.

  "A basic design goal of SGML was to ensure that documents encoded according
to its provisions should be transportable from one hardware and software
environment to another without loss of information."
     **[ REF 1 ]**

  SGML is independent of computer type (it is "platform independent").  It
is an international standard (ISO 8879), not a privately-owned spec for
electronic documents.  It has high archival value.  It is "extensible,"
meaning that it allows and can accomodate change and growth.  Unlike HTML,
it allows users to specify the complex hierarchies associated with database
schema or "object-oriented" work.

  SGML and XML derive from a philosophy that "data belongs to its creators
and that content providers are best served by a data format that does not
bind them to particular script languages, authoring tools, and delivery
engines but provides a standardized, vendor-independent, level playing
field upon which different authoring and delivery tools may freely compete."
     **[ REF 2 ]**

  SGML and XML make possible "the ability to capture and transmit semantic
and structural data."
  For example, "An installation sheet that carries warnings in multiple
languages can be made to show just the ones in the language selected by
the user."  Or, a document which is displayed sorted by last name, can
instantly be displayed sorted by first name.
  "A document containing many annotations can be switched from a mode that
shows only the text, to a mode that shows only the annotations, to a mode
that shows both, just by making a menu selection."  (This is particularly
useful in humanities research.)
     **[ REF 2 ]**


  A large list of SGML projects in academia, including many humanities
computing projects, can be found at
http://www.sil.org/sgml/acadapps.html


  A large list of SGML projects in government and industry can be found at
http://www.sil.org/sgml/gov-apps.html


  A large list of general SGML projects and applications can be found at
http://www.sil.org/sgml/gen-apps.html








  XML
(EXTENSIBLE MARKUP LANGUAGE)

  An "abbreviated" version of SGML, since the full SGML spec is somewhat
intimidating.  XML makes it easy for people to use, understand, and create
markup languages, particularly for Web-based documents.

  XML is developed by a working group of the World Wide Web Consortium (W3C).
The W3C gave "Recommendation" status to the XML (version 1.0) spec in
February 1998.

  "For example, XML will allow online booksellers to use tags such as
'price,' 'number of pages,' and 'author.'  A customer with an XML browser
then can use these specific criteria to sort through the inventory and
arrange the results on the desktop.  Combined with Java programs as well as
new techniques known collectively as 'dynamic HTML,' XML will make browsers
much more flexible."
  "XML was created and developed by the W3C XML Working Group, which includes
key industry players such as Adobe, DataChannel, Hewlett-Packard, Microsoft,
Netscape Communications, and Sun Microsystems, as well as experts in
structured documents and electronic publishing."
  "Several of those companies have released or announced plans [early 1998]
to release Internet software that reads XML."
     **[ REF 3 ]**

  "The XML solution is system-independent, vendor-independent, and proven by
over a decade of SGML implementation experience.  XML merely extends this
proven approach, to document interchange over the Web."
     **[ REF 2 ]**

  "XML provides a standard way for information providers to add custom markup
to information-rich documents, so that complex documents can be rendered
(and published) in a dynamic way."
  "XML provides the means to publish and receive any information, regardless
of format or origin, in any way desired."
     **[ REF 4 ]**



Example:
  A hypothetical XML-based "NPACI Markup Language" document might look as
follows.  Notice the high degree of similarity between a NPACI-ML document
and an HTML document.
        <?XML VERSION="1.0" ?>
        <!DOCTYPE NPACI   SYSTEM "npaci.dtd">
        <NPACI>
           <EDCENTER>
              <PERSON>
                 <DIRECTOR> Dr. Kris Stewart </DIRECTOR>
              </PERSON>
              <PERSON>
                 <ASSISTANT> Dolores Candelario </ASSISTANT>
              </PERSON>
           </EDCENTER>
        </NPACI>
If no DTD were associate with this document, the first line would have been
replaced with  <?XML VERSION="1.0" STANDALONE="YES" ?>  and the
second line would have been omitted.


  In addition to users being able to view NPACI-ML documents on the Web,
NPACI-ML could also be used to "instantly" determine the entire status
of the NPACI project -- e.g., an XML parser could quickly find and count
the number of directors and assistants, or even the number and types of
computer systems.
  Or, the <person> elements might contain short <biography> information,
which could be called up with just a click of the mouse.
  Much better illustrations of SGML/XML's power can be found in IATH's
humanities archives, which will be discussed in Chapter 4 of this Project #1
write-up.








  DTD
(DOCUMENT TYPE DEFINITION)

  "SGML introduces the notion of a 'document type', and hence a 'document
type definition.'  Documents are regarded as having types.  The type of a
document is formally defined by its constituent parts and their structure."
     **[ REF 1 ]**

  The most well-known document type is the "HTML" document.
  SGML's and XML's specs allow users to create their own document types.
For example, one humanities researcher created an XML-based "PLAY" document
type, for Shakespeare's plays.  Typical markup tags embedded into the
text of the plays include <persona>, <scene>, <speaker> and <speech>.

  SGML requires that each document be associated with a DTD.
  For XML documents, DTDs are optional, but only if the documents are
"well formed" (this will be defined shortly).

  DTDs specify allowable tags, such as <poemtitle>, and allowable nesting
of tags.
  The purpose of a DTD is to formally define a new document type, and to
make it possible for software to properly parse a document's content.


Example:
  The following DTD is for a hypothetical XML-based "NPACI Markup Language."
  The DTD can be embedded in-line in a NPACI document.  Or, the DTD can
be saved in a file "npaci.dtd", and the NPACI document can link to it
remotely (as shown in the "Example" document in the "XML" Section above).
  <!DOCTYPE NPACI [
  <!ELEMENT NPACI (EDCENTER)*>
  <!ELEMENT EDCENTER (PERSON)>
  <!ELEMENT PERSON (DIRECTOR,ASSISTANT)>
  <!ELEMENT DIRECTOR (#PCDATA)>
  <!ELEMENT ASSISTANT (#PCDATA)>
  ]>


Example:
  The following DTD is for a sample SGML-based literary document type which
is given in *[REF 1]*
  <!DOCTYPE anthology [
  <!ELEMENT anthology       - -  (poem+)           >
  <!ELEMENT poem            - -  (title?, stanza+) >
  <!ELEMENT stanza          - O  (line+)           >
  <!ELEMENT (title | line)  - O  (#PCDATA)         >
  ]>








  "VALID" AND "WELL-FORMED" DOCUMENTS

  SGML requires that each document be associated with a DTD.
  DTDs are optional for XML documents, provided that the documents are
"well formed."  (This is one of the lax rules that makes XML easier to use
than SGML.)

  An XML document is "WELL-FORMED" if.....
  .....it uses starting tags <tag> and ending tags </tag>
.....attribute values are in quotes.....empty element tags such as
<ParagraphBreak> are rendered as either <ParagraphBreak/> or else with
a corresponding ending tag </ParagraphBreak> added immediately after it
.....tags are nested properly, not overlapping.....A few other, more
obscure rules.

  A document is "VALID" if it is associated with a DTD, adheres to the
DTD's markup rules, and is well-formed.

  "A well-formed XML document is unambiguous, so that a browser or editor
can read the tags and create a tree of the hierachical structure
without having to read its Document Type Definition."
     **[ REF 4 ]**








  STYLE SHEETS

  A style sheet is a file or set of instructions which tell a Web browser
how a document's elements are to be displayed -- e.g., <header> text
should be displayed in green color and with 80-point Times-Roman font, etc.


Example:
  H1 { font-size:80pt; color:green; font-weight:bold; }
  When properly embedded in a file, or properly linked to as a remote file,
this will cause <H1> header text to be displayed in 80-point, green,
bold font.








  CSS
(CASCADING STYLE SHEETS)

  CSS are the style sheets generally associated with HTML documents.
However, the XML in Microsoft's Internet Explorer uses CSS, rather
than XSL style sheets.  Netscape Navigator/Communicator 5.0's XML, due out
later this year, will also use CSS to convert XML data into HTML display,
but Netscape says that they are working to integrate XSL into the browser as
soon as possible.

  Style sheets are found only in the 4+ browsers (Netscape Navigator 4 and
later, and Microsoft Internet Explorer 4 and later).
  These are the "CSS-capable" browsers.

  "The HTML4 spec states that CSS can be written inline or specified as
an external file."
     **[ REF 5 ]**

  "As the term cascading style sheets implies, more than one style sheet
can be used on the same document, with different levels of importance.
If you define conflicting styles for the same HTML tag, the innermost
definition -- the one closest to the tag -- wins."
     **[ REF 6 ]**

  Appendix 1 (of this Project #1 write-up) is a primer on writing CSS.








  CSS1, CSS2

  "Cascading Style Sheets, Level 1" and "CSS, Level 2."

  CSS2 is the newest spec for style sheets.

  "In December 1996, the CSS1 specification became a W3C Recommendation."
     **[ REF 7 ]**

  The term "cascading" implies that "more than one style sheet can "cascade"
together to produce the final look of the document: individual style sheets
from different sources can be combined."
     **[ REF 7 ]**

  "In May 1998, the CSS2 specification was released as a W3C Recommendation.
CSS2 gives content creators, designers and readers the powerful tools they
need to realize the full potential of their HTML and XML documents.  CSS2
includes all the power of CSS1, and adds enhancements in several areas to
make the Web more appealing for both content providers and users.  Although
originally developed for HTML, CSS has been designed to allow you to style
XML documents also."
  "The CSS2 Recommendation is based upon CSS1 and is a prerequisite for the
Document Object Model (DOM), W3C's platform- and language-neutral interface,
which allows programs and scripts to dynamically access and update the
content, structure, and style of documents."
     **[ REF 7 ]**

  CSS1 is supported by the 4+ browsers (Navigator 4+ and MSIE 4+).
However, "there are some disparities where CSS1 features have not been fully
or correctly implemented."
     **[ REF 7 ]**


  A condensed version of W3C's CSS1 spec can be found in *[ REF 6 ]*.
It lists the most important information about each CSS property and its
available values.  This "CSS Reference Table" is located at
http://builder.cnet.com/Authoring/CSS/table.html








  CSS POSITIONING

  "An extension to CSS1 that lets you control an object's precise
position on the page.  You can also specify whether an object is visible
or hidden, and even layer objects on the page.  Although not yet a W3C-
recommended standard, CSS positioning is a working draft, stable enough
for public discussion, although it may still change before it's final."
     **[ REF 6 ]**

  "CSS positioning is already supported by both Netscape Navigator 4.0 and
Microsoft Internet Explorer 4.0."
     **[ REF 6 ]**

  "It works like this.  When a browser renders an object on the page with
CSS positioning, it places it into an invisible rectangle, called a bounding
box.  You can set the box's exact distance from the top and/or left edges of
the browser window, or you can offset the box from other elements on the
page.  You can also specify the height and width of the box.  You can even
layer objects on top of one another.  And since objects can overlap, CSS
positioning includes clipping features that let you cut off an area of an
element -- for example, to have a top object reveal another one beneath it.
Finally, you can make entire objects visible or invisible."
     **[ REF 6 ]**


Example:
  H1 { position: absolute; top: 150px; width: 200px; height: 200px }
  Will place <H1> header text inside a box which is 150 pixels from the
top of the page and is 200 pixels wide by 200 pixels high.
     **[ REF 6 ]**


Example:
  A better example uses in-line styles and <DIV> and <SPAN> tags.
  <DIV style="position:absolute; top:150px; width:200px; height:200px;
background-color:red">This is text in a red 200-by-200-pixel box that is
150 pixels from the top of the window.<DIV>
     **[ REF 6 ]**








  DHTML
(DYNAMIC HTML)

  "Combines CSS, CSS positioning and -- most critically -- the
document object model (DOM) to let you create dynamic and interactive
pages.  Of these, only CSS1 is a W3C-recommended standard, so right
now a dynamic page designed for IE won't work in Communicator, and
vice versa.  Standardization of the DOM -- the interface that allows
developers to control individual objects on a Web page -- is under
way but by no means complete."
     **[ REF 6, late 1997 ]**








  DSSSL
(DOCUMENT STYLE AND SEMANTICS
SPECIFICATION LANGUAGE)

  The international standard for style sheets for SGML documents.

  SGML uses DSSSL the same way that HTML uses CSS.








  XSL
(EXTENSIBLE STYLE SHEET LANGUAGE)

  The syntax for style sheets for XML documents.

  "We expect that CSS will be used to display simply-structured XML
documents, and XSL will be used where more powerful formatting capabilities
are required or for formatting highly structured information such as XML
structured data or XML documents that contain structured data."
     **[ REF 8, 1997 ]**

  XSL is much more powerful than CSS.  However, according to the W3C, whose
Working Groups are developing XSL, "the syntax for XSL is still under
development and subject to change."
     **[ REF 7, June 1998 ]**

  Note: W3C published the first "Working Draft" of the XSL 1.0 spec,
on August 18, 1998.  (After attaining "Working Draft" status, a W3C spec
must then attain "Proposed Recommendation" and "Recommendation" status.)








  THE WORLD WIDE WEB CONSORTIUM (W3C)

  http://www.w3.org

  They develop the "recommended" specs for many Web-related things, such
as XML, XSL, CSS, etc.

  "The W3C was founded in October 1994 to lead the World Wide Web to its
full potential by developing common protocols that promote its
evolution and ensure its interoperability.  We are an international
industry consortium, jointly hosted by the MIT Laboratory for Computer
Science (in the U.S.), the Institut National de Recherche en Informatique
et en Automatique (in Europe), and the Keio University Shonan Fujisawa
Campus (in Japan).
  "Services provided by the Consortium include: a repository of information
about the World Wide Web for developers and users; reference code
implementations to embody and promote standards; and various prototype and
sample applications to demonstrate use of new technology.
  "Initially, the W3C was established in collaboration with CERN, where the
Web originated, with support from DARPA and the EC.
  "The Consortium is led by Tim Berners-Lee, Director and creator of the
World Wide Web, and Jean-Francois Abramatic, Chairman.
  "W3C is funded by Member organizations, and is vendor neutral, working with
the global community to produce specifications and reference software that is
made freely available throughout the world."
  "The Consortium attempts to find common specifications for the Web so that
through dramatic and rapid evolution, many organizations can work in their
own fields and build on top of the global information space which is
the web."
     **[ REF 9 ]**

  "Specifications developed within the Consortium must be formally approved
by the Membership.  Consensus is reached after a specification has proceeded
through the review stages of Working Draft, Proposed Recommendation,
and Recommendation.
     **[ REF 10 ]**








  BIBLIOGRAPHY

REF 1
     "A Gentle Introduction to SGML"
     http://www-tei.uic.edu/orgs/tei/sgml/teip3sg/index.html

REF 2
     "XML, Java, and the future of the Web"
     By Jon Bosak, Sun Microsystems
     http://sunsite.unc.edu/pub/sun-info/standards/xml/why/xmlapps.htm

REF 3
     "W3C Makes XML a Standard"
     Erich Luening, CNET NEWS.COM
     http://www.news.com/News/Item/0,4,19008,00.html

REF 4
     "A Brief Introduction to XML"
     http://?????????

REF 5
     "WebDeveloper.com's Guide to Cascading Style Sheets"
     By Scott Clark
     http://www.webdeveloper.com/categories/html/html_css_1.html

REF 6
     "Get Started With Cascading Style Sheets"
     By Matt Rotter and Charity Kahn
     http://www.cnet.com/Content/Builder/Authoring/CSS/

REF 7
     "Style Sheets Activity"
     By the W3C, June 1998

REF 8
     "A Proposal for XSL"
     By Microsoft Corp., ArborText, and Inso Corp., 1997

REF 9
     "About The World Wide Web Consortium"
     By the World Wide Web Consortium
     http://www.w3.org/Consortium/

REF 10
     "W3C Backgrounder : Recommendation Process"
     By the World Wide Web Consortium
     http://www.w3.org/Press/Backgrounder.html