1. Linda Schmandt Structured Text & XML in Medicine 16 Jan 2004

2. 2 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

3. 16 Jan 2004 3 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”).

4. 16 Jan 2004 4 Separation of content & formatting: content 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

5. 16 Jan 2004 5 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

6. 16 Jan 2004 6 History, cont’d 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

7. 16 Jan 2004 7 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 industry’s terms and expressions, e.g. Aircraft maintenance documentation Power plant documentation Usually large scale, long term

8. 16 Jan 2004 8 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.

9. 16 Jan 2004 9 HTML Developed 1992-1995 (HTML 2.0) Purpose: To codify the representation of documents on the WWW

10. 16 Jan 2004 10 Why XML? Tools that support SGML are more expensive than those that support HTML because of: Smaller market for vendors Relative complexity of definition It’s fairly complicated to create an SGML DTD or document without a tool. Too complex to deliver SGML over the web

11. 16 Jan 2004 11 Why not just use HTML? Fixed set of tags: can’t represent complex structure Little capacity to represent content Optimized for one kind of presentation (browser) Therefore, we need a simplified form of SGML.

12. 16 Jan 2004 12 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.

13. 16 Jan 2004 13 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.

14. 16 Jan 2004 14 Markup language comparison FeatureSGMLHTMLXML Facilitates delivery in multiple formatsYNY Widely available toolsYYN Inexpensive toolsNYUnder dev’t Enables rich tagging of document structure and semantics YNY Documents must reference a DTDYFixed set of tags DTD / Schema optional.

15. 16 Jan 2004 15 SGML / XML Differences FeatureSGMLXML End tags are requiredNY Linking across/among documents NY Data typing is possibleY, but requires Annex K support – usually not supported by vendors Y, but requires an XML Schema (not a DTD)

16. 16 Jan 2004 16 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

17. 16 Jan 2004 17 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)

18. 16 Jan 2004 18 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

19. 16 Jan 2004 19 Resources An overview of SGML resources: http://www.w3.org/MarkUp/SGML/ http://www.w3.org/MarkUp/SGML/ The authoritative guide: Goldfarb CF and Rubinsky Y (contributor). The SGML Handbook. 1991. http://www.sgmlopen.org