1. Beyond HTML: Extensible Markup Language
Timothy W. Cole
Grainger Engineering Library Information Center University of Illinois at Urbana-Champaign
American Association of Law Libraries 19 July 2000

2. Ordered Hierarchy of Content Objects A Definition of Text in Computer Terms
Premise: A Text is the Sum of its Components
So a <BOOK> Could Be Defined as Containing: <FRONT_MATTER> <CHAPTER>s <BACK_MATTER>
<FRONT_MATTER> Could Contain: <BOOK_TITLE> <AUTHOR>s <PUBLISHER>
While Each <CHAPTER> Could Contain: <CHAPTER_TITLE> <SECTION>s
And Each <SECTION> Could Contain: <SECTION_TITLE> <PARAGRAPH>s
Components Chosen Reflect Anticipated Use

3. Ordered Hierarchy of Content Objects (continued)
OHCO is a Useful, Albeit Imperfect Model
More Powerful Than Model of Text as a Stream of Characters & Formatting Instructions
Does Not Allow for Overlapping Content Objects
OHCO Model is Inherent in XML, HTML
XML Designed for Descriptive Content Objects, Not Presentational Content Objects
XML Syntax is Fixed, But Semantics is Extensible

4. XML Basics: Markup & Content
Consider: Would Display As: <?xml version='1.0' ?> Colè, Tim <!-- This is an Example --> <author sequence='first'> <LName> Colè </LName>, <FName> Tim </FName> </author>
This example illustrates:
XML Processing Instructions
XML Comments (Ignored by XML Applications)
XML Element Markup, Including an Attribute
XML Content, Including an Entity

5. XML Basics (continued)
“Well-Formed” XML Rules:
XML Element Markup is Case-Sensitive
All XML Tags Must Be Closed
Hierarchical Nesting; No Overlapping Elements
All XML Attribute Values Must Be Quoted
Enforces Stricter Syntax than HTML
Facilitates Fast, Efficient Parsing
Extensible Semantics Provide Flexibility
“Well-Formed” More Lightweight Than SGML

6. Is It Valid Or Well-Formed? When Does It Matter?
All Web Browsers Need Is Well-Formed
XML Authoring Tools Need To Validate
Otherwise Tower of Babel Ensues
Indexing Agents & Schema-Specific Rendering Agents May Need To Validate
Illustrations:
Malformed XML
Well-Formed But Invalid XML
Valid XML

7. Library Uses of XML: Using XML for Primary Sources
Facilitates Searching
Full-Text Searching & Field-Specific Searching
More Meaningful Proximity Searching
Better Retrieval / Browsing
Selective Views / Suppression of Personal Data
Re-Ordered & Piecemeal Views
Illustration -- Illinois Agronomy Handbook
Search
Browsing

8. Library Uses of XML: XML for Metadata & Wrapping
Facilitates Interchange, Normalization, ...
Simpler than Fixed Fields, Record Headers, Etc.
XML Implementations of Metadata Standards, e.g.: RDF, EAD, DC, FGDC, US-MARC
Easier Routing / Handling of Specialized Content
In Combination with Primary Source XML
Automatic Extraction of Metadata From Source
Facilitates Authority Control

9. Library Uses of XML: XML for Document Management
Smarter Documents
XML Namespaces -- Integrating Multiple XML Schemas (Including XHTML)
Rights Management, Technical Requirements,…
Facilitates Enhanced Linking Between Docs.
Creation of Links From Marked Up Content
Easy to Add or Modify Links Over Time
XLink & XPointer Promise More Robust Linking
Metadata File from Illinois DLIB Testbed
Schema Integrates RDF, DC, & Project Design

10. Components of XML Implementations DTDs & XML Schemas
Use Either to:
Define Content Models
Declare Attributes & Entities
DTDs Inherited from SGML
DTDs Themselves Not Well-Formed XML
Limits on Detail of Content Model Definitions
Minimal Data Typing
XML Schemas Are Well-Formed XML
Data Typing & Better Content Models Supported
Not Yet in Widespread Use

11. Components of XML Implementations Encoding & Entities (Using Characters Not on Your Keyboard)
Computers Use 1s and 0s, but Characters form the Basis of Human-Readable Texts
Coded Character Sets (CCS) Assign Integer Values to Characters -- ASCII, ISO 8859, Unicode
Character Encoding Schemes (CES) Map Those Integers to Bytes -- 7-bit, 8-bit, UTF-8
Bytes Are Then Rendered as Glyphs by Your Computer, Using Font Appropriate to CCS/ CES
Font Unavailable Or CCS/CES Misunderstood Results in Incorrect Character(s) on Screen

12. Components of XML Implementations Encoding & Entities (continued)
Common Ways to Deal With This Problem:
Select CCS/CES Appropriate to Language
Use Default CCS/CES, but Override Default Font
Use XML/HTML Named or Numeric Entity
HTML Understands Non-Extensible Set of Named Entities
XML Understands Numeric Entities Corresponding to Unicode CCS, All Named Entities Must Be Declared in DTD
Use Unicode for CCS, UTF-8 for CES - XML Defaults
An Illustration in HTML

13. Components of XML Implementations Presentation - CSS Style Sheets
XML Content Objects Have No Style
Use Cascading Style Sheets (CSS) Work Like CSS for HTML, Except:
Must Be Explicit About Everything
No Special Treatment of Class & ID Attributes
Attach CCS to XML Using Special XML PI
CSS Does Define Formatting
CSS DOES NOT Reorganize or Add Content
Simple XML-CSS Example; The CSS Used

14. Components of XML Implementations Transformations - XSLT Style Sheets
Some Characteristics of XSLT Style Sheets
XSLT Files Are Well-Formed XML
XSLT Transform to Another Schema, Or to XHTML
XSLT Objects Have Implicit Functionality
Attach XSLT To Document Using XML PI
XSLT Can Reorganize & Add Content
Still Need CSS for Presentation -- CSS Style Sheets Work on the Output of XSLT Processing
Supplement XSLT With Script To Manipulate & Modify Actual Content
Simple XSLT Example; The XSLT Style Sheet

15. The State-of-the-Art in XML Tools
XML Authoring
Add-Ons to Established Word Processors, e.g.: WordPerfect 9 / WordPerfect 2000
Tools With SGML Roots, e.g.: ArborText’s Epic (was Adept) Editor SoftQuad’s XMetaL Editor
New XML Tools, e.g.: Vervet Logic’s XMLPro Extensibility’s XML Authority / XML Turbo
So Far, There Are Fewer Authoring Tools Customized for Specialized XML Schemas

16. The State-of-the-Art in XML Tools (continued)
XML Presentation Tools:
Latest Releases of Netscape Navigator/Mozilla, and Microsoft’s Internet Explorer Support XML -- But Support is Generic, Partial, & Uneven
Plug-Ins, Standalones Available / In Work for Advanced XML Schemas (CML, MML, VML,…)
XML Database Integration Tools:
Add-Ons to Established DBMS Available/In Work Microsoft SQL Server-XML Technology Preview
Illustration; With Query & CSS; XML Source File;
XML Query Language Specification In Work

17. Developing XML Applications: The Politics of XML
Evolution of XML
XML Formalized as W3C Recommendation 2/98
Numerous Ancillary Specs Released & In Work Namespaces, XSLT, XLink/XPointer, XML Signature
Numerous Early Implementors (Chemistry, Biology, Multimedia, Metadata)
Prerequisites for Community Implementations
Identify Target(s) of Opportunity
Define Horizontal & Vertical Content Objects
Consensus Building & Community Buy-In
Test Implementations & Tool Building

18. Developing XML Applications: The Politics of XML (continued)
Status of XML In Legal Community
LegalXML Has Identified Targets Begun Process of Defining Content Objects & Building Consensus
Progress in Some Areas, e.g.: Court Filing (see also XML Court Interface)
Less Visible Progress in Other Workgroups, e.g.: Reference, Public Law, Users
Presence (& Vested Interests) of Extensive Non-XML Legal Automation Systems In Place Lessens Motivation

19. Developing XML Applications: The Politics of XML (continued)
Status of XML In Publishing & Libraries
Extensive XML Work in Metadata Unfortunately Has Led to Competing Stds.
Many Publishers Have Been Using SGML for a Decade or More -- But Only Internally
Perceived Tradeoff (probably overrated): Publicly Releasing Primary Sources in XML vs. Control of Product & Marketplace
Problems with Early SGML Web Experiments
No One Wants to be First But No One Wants to be Last Either

20. Future Directions Continued Evolution of Standards, Tools
Continued Development of Community Implementations -- Selected Disciplines
Increased Use of XML Behind the Scenes
Carryover from SGML Trends
Integration of XML with Databases
XML Unlikely to Replace HTML, Other Document Formats, But Will Co-Exist
Magnitude of Role in Law Libraries Uncertain, but Likely to Have At Least Some Role