SGML

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ltSGMLgt

• Linda Schmandt
• Structured Text XML in Medicine
• 16 Jan 2004

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SGML

• Standard Generalized Markup Language
• International standard for defining descriptions
  of structure and content in electronic documents
  (ISO 8879)
• Main contributions
• Separation of content and formatting
• A way of creating markup languages customized
  for particular documents but still readily
  interchangeable

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Separation of content formatting formatting

• cook (kuk) ME coke cook 1. (vt) To prepare
  for eating by providing heat. 2. (vt) To prepare
  or treat by heating. 3. (n) A person who prepares
  food for eating.
• cook kuk
• trans 1. To prepare for eating by providing
  heat. 2. To prepare or treat by heating.
• noun 3. A person who prepares food for eating.
• (from ME coke cook).

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Separation of content formatting content

• lt entry gt
• lt headword gt cook
• lt pronunciation gt kuk
• lt etymology gt lt lang gt ME lt word gt coke lt
  gloss gt cook
• lt /etymology gt
• lt meanings gt lt sub gt lt no gt 1 lt pos gt vt lt defn
  gt to prepare for eating by providing heat lt /sub
  gt
• lt sub gt lt no gt 2 lt pos gt vt lt defn gt to
  prepare or treat by heating lt /sub gt
• lt sub gt lt no gt 3 lt pos gt n lt defn gt a person
  who prepares food for eating lt /sub gt lt /entry gt

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History

• 1969 IBM research project to integrate law
  office information systems.
• Team Goal Allow the text editing, formatting,
  and information retrieval subsystems to share
  documents.
• Team Charles Goldfarb, Edward Mosher, Raymond
  Lorie
• Deliverable Generalized Markup Language (GML)
• Innovation A formally-defined document type
  with an explicit nested element structure

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History, contd

• 1974 Goldfarb invents Standard Generalized
  Markup Language (SGML)
• 1978 The American National Standards Institute
  (ANSI) committee on Information Processing
  establishes the Computer Languages for the
  Processing of Text committee Goldfarb is asked
  to lead a project for a text description language
  standard based on GML.
• 1986 SGML becomes ISO Standard 8879

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SGML Applications

• SGML does not provide a fixed set of tags, but
  rather a syntax for creating your own tags.
• Many industry-specific common tag sets to
  interchange information using the industrys
  terms and expressions, e.g.
• Aircraft maintenance documentation
• Power plant documentation
• Usually large scale, long term

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Example SGML Applications

• Computer-aided Acquisition and Logistics Support
  (CALS) documentation component (1987)
• Department of Defense and representatives of
  military contractors and military commands
• Electronic Manuscript Project (1983)
• Association of American Publishers (AAP)
• For book, journal, and article creation, to
  support manuscript interchange between authors
  and their publishers, among other uses
• Includes optional element definitions for complex
  tables and scientific formulas.

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HTML

• Developed 1992-1995 (HTML 2.0)
• Purpose To codify the representation of
  documents on the WWW

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Why XML?

• Tools that support SGML are more expensive than
  those that support HTML because of
• Smaller market for vendors
• Relative complexity of definition
• Its fairly complicated to create an SGML DTD or
  document without a tool.
• Too complex to deliver SGML over the web

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Why not just use HTML?

• Fixed set of tags cant represent complex
  structure
• Little capacity to represent content
• Optimized for one kind of presentation (browser)
• Therefore, we need a simplified form of SGML.

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Requirements on XML

• Easy, quick, inexpensive document
• creation
• processing
• presentation
• re-use
• Allows user to create a customized set of tags
• Compatibility with HTML
• Power of SGML
• Significantly less complex than SGML The paper
  that describes the syntax of XML is only about 30
  pages long, and can be understood by any web page
  designer.

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SGML and XML similarities

• Metalanguages for defining document structure and
  content
• Logically and functionally identical SGML lets
  you represent the same information, but in more
  different ways
• XML is a simplified subset of SGML, optimized for
  the Web environment.

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Markup language comparison
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SGML / XML Differences
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SGML / XML Differences

• Typical use
• SGML is publishing-oriented large volumes of
  long-lived information
• XML is data-processing-oriented often smaller
  volumes of short-lived information e.g. banking
  system front-end that can receives XML-based
  financial transactions and converts them into
  deposit and withdrawal instructions
• Style Sheets for Delivery
• XML Has a Standard for Style Sheets and XSL is
  required for browser output (to convert XML to
  HTML)
• SGML Implementations of Style Sheets vary.
• Re-use of Content
• XML Can re-use portions of documents, conforming
  to different DTD/Schemas together
• SGML Re-use of portions of documents together as
  one only if they conform to the same DTD

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Sample features in SGML but not XML

• Exclusions allow you to specify exceptions in
  your content model, for example
• paragraphs can contain appendix references except
  when those paragraphs appear in the appendix.
• footnotes are printed in a specified way except
  when they appear within footnotes
• AND content models All elements must be used,
  but they can appear in any order. (Available in
  XML Schemas, but not XML DTDs)

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Markup language development timeline

• 1986  SGML ISO 8879-1986
• 1995   HTML 2.0
• 1996  first XML Working Draft
• Jan 1997  HTML 3.2
• Dec 1997  
• XML 1.0 Proposed Recommendation
• HTML 4.0 Recommendation
• 1998   XML 1.0 recommendation

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Resources

• An overview of SGML resources
  http//www.w3.org/MarkUp/SGML/
• The authoritative guide
• Goldfarb CF and Rubinsky Y (contributor). The
  SGML Handbook. 1991.
• http//www.sgmlopen.org