Beyond HTML: Extensible Markup Language

1
Beyond HTMLExtensible Markup Language

• Timothy W. Cole
• Grainger Engineering Library Information
  CenterUniversity of Illinois at Urbana-Champaign
• American Association of Law Libraries19 July
  2000
• t-cole3_at_uiuc.edu
• http//dli.grainger.uiuc.edu/Publications/TWCole/A
  ALL_2000/

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Ordered Hierarchy of Content ObjectsA Definition
of Text in Computer Terms

• Premise A Text is the Sum of its Components
• So a ltBOOKgt Could Be Defined as
  ContainingltFRONT_MATTERgt ltCHAPTERgts
  ltBACK_MATTERgt
• ltFRONT_MATTERgt Could ContainltBOOK_TITLEgt
  ltAUTHORgts ltPUBLISHERgt
• While Each ltCHAPTERgt Could ContainltCHAPTER_TITLE
  gt ltSECTIONgts
• And Each ltSECTIONgt Could ContainltSECTION_TITLEgt
  ltPARAGRAPHgts
• Components Chosen Reflect Anticipated Use

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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 Aslt?xml
  version'1.0' ?gt Colè, Tim lt!-- This is
  an Example --gtltauthor sequence'first'gtltLNamegt
  Colegrave lt/LNamegt,ltFNamegt Tim lt/FNamegt
  lt/authorgt
• This example illustrates
• XML Processing Instructions
• XML Comments (Ignored by XML Applications)
• XML Element Markup, Including an Attribute
• XML Content, Including an Entity

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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

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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

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Library Uses of XMLUsing 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

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Library Uses of XMLXML 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

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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

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Components of XML ImplementationsDTDs 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

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Components of XML ImplementationsEncoding
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

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Components of XML ImplementationsEncoding
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

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Components of XML ImplementationsPresentation -
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

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Components of XML ImplementationsTransformations
- 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

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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.ArborTexts Epic
  (was Adept) EditorSoftQuads XMetaL Editor
• New XML Tools, e.g.Vervet Logics
  XMLProExtensibilitys XML Authority / XML Turbo
• So Far, There Are Fewer Authoring Tools
  Customized for Specialized XML Schemas

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The State-of-the-Art in XML Tools (continued)

• XML Presentation Tools
• Latest Releases of Netscape Navigator/Mozilla,
  and Microsofts 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
  WorkMicrosoft SQL Server-XML Technology Preview
• Illustration With Query CSS XML Source File
• XML Query Language Specification In Work

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Developing XML ApplicationsThe Politics of XML

• Evolution of XML
• XML Formalized as W3C Recommendation 2/98
• Numerous Ancillary Specs Released In
  WorkNamespaces, 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

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Developing XML ApplicationsThe 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

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Developing XML ApplicationsThe Politics of XML
(continued)

• Status of XML In Publishing Libraries
• Extensive XML Work in MetadataUnfortunately 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 FirstBut No One Wants to be
  Last Either

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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