Why use XML

1
Why use XML?
2
Suns slogan

• Java XML
• portable programs portable data

3
Markup

• Information added to data to enhance its
  meaning
• Identification of parts, boundaries and
  relationships of elements within documents
• Identification of attributes

Without markup, most documents appear as
meaningful to machines as this document does to
humans
4
Whats wrong with HTML?

• lthtmlgt
• ltheadgt
• lttitlegt
• Martins page
• lt/titlegt
• lt/headgt
• ltbody bgcolourffffffgt
• ltp aligncentergt
• Some text or other
• lt/pgt
• lt/bodygt
• lt/htmlgt

• HTML is the most successful electronic publishing
  language ever invented, but ....
• .... HTML is for presentation, not content,
  limiting its applicability

5
XML example

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Bogdanov"gt
• ltLecturegtPropslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

6
XML example

• Encodes
• boundaries

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Bogdanov"gt
• ltLecturegtPropslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

7
XML example

• Encodes
• boundaries
• roles
• eg course v lecture

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Bogdanov"gt
• ltLecturegtPropslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

8
XML example

• Encodes
• boundaries
• roles
• eg course v lecture
• positions

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Bogdanov"gt
• ltLecturegtPropslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

9
XML example

• Encodes
• boundaries
• roles
• eg course v lecture
• positions
• containment
• eg lecture is part of course

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Bogdanov"gt
• ltLecturegtPropslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

10
XML example

• Encodes
• boundaries
• roles
• eg course v lecture
• positions
• containment
• eg lecture is part of course
• attributes
• eg title

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Bogdanov"gt
• ltLecturegtPropslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

11
A brief history of markup

• GML Generalised Markup Language
• Developed in 60s and 70s by IBM
• Used for IBM technical manuals
• SGML Standardised GML
• 70s, 80s with ANSI standard in 1983
• Flexible and very general, but difficult and
  costly
• HTML
• Early 90s compact markup for hypertext docs
• Now seen as a step backwards
• XML

12
XML is

• Simpler than SGML
• More flexible than HTML
• An application of SGML
• Not a markup language, but a toolkit
• however, common to refer to documents as being
  written in XML
• Surrounded by a family of technologies which
  extend its use (eg transformation)

13
XML features

• Represent most kinds of information,
  unambiguously (unlike HTML)
• Easily customizable
• Supports internationalization through UNICODE
• Allows validation of documents
• Easy to read by humans and machines
• Open standard, managed by W3C

14
Applications of a better data format

• Better search engines
• find all places selling X
• Customised data presentation from a single source
• HTML
• WML (wireless markup language)
• PDF
• Reliable information exchange
• CML (chemical structures)
• VoxML (voice)
• B2B transactions of all types
• MathML
• etc

15
XHTML
Source http//www.w3.org/TR/xhtml1/
16
MathML example

• Can be used for display or calculations
• Source http//www.dessci.com/support/tutorials/ma
  thml/default.stm

17
SVG (scalable vector graphics)

• SVG benefits
• Zooming 
• Text stays text. Text in SVG images remains
  editable and searchable
• Small file size 
• Display independence
• Interactivity and intelligence

Source http//www-106.ibm.com/developerworks/educ
ation/transforming-xml/xmltosvg
18
VoiceXML
Source http//www.w3.org/TR/voicexml20/dml1.3.1
19
DocBook
Source http//nis-www.lanl.gov/rosalia/mydocs/do
cbook-intro/get-going.html
20
Apache documentation
Source http//jakarta.apache.org/ecs/index.html
21
WML
Source http//www.wap-uk.com/Developers/Tutorial.
htm
22
A closer look at XML documents
23
Simple example

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

24
Document prolog

• indicates that this document is marked up in XML
• Format
• lt?xml propvalue ?gt
• Param values must be quoted with single or double
  quotes (unlike HTML)

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

25
Document type declaration

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

• Specifies validation root
• Format
• lt!DOCTYPE root-element
• SYSTEM dtdgt
• DTD is optional (see later)

26
Elements

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

• Building blocks of XML documents
• One root element
• Format
• ltname attvalue gt
• content
• lt/namegt
• Or
• ltname attval /gt
• None-empty elements must have a closing tag
  (unlike HTML)

27
Elements

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

• Elements may contain other elements
• An elements start and end tags must reside
  within the same parent (ie boxes cannot overlap)

28
Attributes

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

• Used to identify specific elements, or to
  elaborate elements
• Values must be quoted (single or double)
• Not always clear whether to use attributes or
  elements

29
Attributes or elements?

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

• Attributes shouldnt really hold content
• Attribute order is ignored, whilst element order
  is significant
• Attributes values can be restricted (see DTDs
  later)
• Use attributes as unique refererences if needed

30
An XML document is a tree

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

Curriculum
Course
Course
Lecture
Lecture
Lecture
Lecture
Lecture
31
with content at its leaves

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

Curriculum
Course
Course
Lecture
Lecture
Lecture
Lecture
Class diagrams
Lecture
Use cases
Sets
Propositions
Predicates
32
and attributes

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE Curriculum SYSTEM "Curric.DTD"gt
• ltCurriculumgt
• ltCourse Title"Z" Lect"Kyrill Bogdanov"gt
• ltLecturegtPropositionslt/Lecturegt
• ltLecturegtPredicateslt/Lecturegt
• ltLecturegtSetslt/Lecturegt
• lt/Coursegt
• ltCourse Title"UML" Lect"Marian Gheorge"gt
• ltLecturegtUse Caseslt/Lecturegt
• ltLecturegtClass Diagramslt/Lecturegt
• lt/Coursegt
• lt/Curriculumgt

Curriculum
Course
Course
TitleUML Lect
TitleZ Lect
Lecture
Lecture
Lecture
Lecture
Class diagrams
Lecture
Use cases
Sets
Propositions
Predicates
33
Well-formedness

• Element containing text or elements must have
  start and end tags

Good ltcurriculumgt ltcoursegtZlt/coursegt
ltcoursegtJavalt/coursegt lt/curriculumgt
Bad ltcurriculumgt ltcoursegtZ
ltcoursegtJava lt/curriculumgt
34
Well-formedness

• Element containing text or elements must have
  start and end tags
• Empty elements tag must close with /gt

Good ltgraphic filenameicon.png/gt
Bad ltgraphic filenameicon.pnggt
35
Well-formedness

• Element containing text or elements must have
  start and end tags
• Empty elements tag must close with /gt
• Attributes must be in quotes

Good ltcourse TitleJavagt ltcourse TitleZgt
Bad ltcourse TitleUMLgt
36
Well-formedness

• Element containing text or elements must have
  start and end tags
• Empty elements tag must close with /gt
• Attributes must be in quotes
• Elements must not overlap

Good ltcurriculumgt ltcoursegtZlt/coursegt lt/curri
culumgt
Bad ltcurriculumgt ltcoursegtZ
lt/curriculumgt lt/coursegt
37
Well-formedness

• Element containing text or elements must have
  start and end tags
• Empty elements tag must close with /gt
• Attributes must be in quotes
• Elements may not overlap
• Markup chars must not appear in parsed content

Good ltequationgt5 lt 2lt/equationgt
Bad ltequationgt5 lt 2lt/equationgt
38
Well-formedness

• Element containing text or elements must have
  start and end tags
• Empty elements tag must close with /gt
• Attributes must be in quotes
• Elements may not overlap
• Markup chars must not appear in parsed content
• Element names start with letters or _, and
  contain letters, numbers, -, . and _

Good ltcurriculumgt lt_coursegt lttime-slotgt ltbook
.chaptergt
Bad lt1examplegt ltthe firstgt ltbookchaptergt
39
Why the rules?

• Unlike HTML, an arbitrary XML document doesnt
  necessarily have a grammar
• eg HTML knows that a ltpgt cannot contain another
  ltpgt, so the end tag is optional

40
Pros and cons of adding a grammar

• CONS
• More effort during development
• Grammars need to be maintained
• Can slow down processing
• Need to learn a new syntax (although it is
  trivial for CS)

• PROS
• Grammars enables documents to be validated
• Enforce restrictions such as required fields,
  limited choices
• Serves as a clear description of the syntax for
  users and developers
• Can act as a standard eg XHTML
• Good for debugging

41
Document Type Definition (DTD)

• lt!ELEMENT Curriculum (Course)gt
• lt!ELEMENT Course (Lecture)gt
• lt!ATTLIST Course
• Title CDATA REQUIRED
• Lect CDATA REQUIRED
• gt
• lt!ELEMENT Lect (PCDATA)gt

• A DTD is a sequence of declarations
• Doesnt conform to XML syntax
• Easy to understand for CS
• PCDATA keyword stands for parsed character
  data and means that the textual content will be
  parsed to look for XML entities (see later)

42
Element definitions

• lt!ELEMENT article
• (title,subtitle?,author,(paratablelist)
  ,biblio?)
• gt

43
Attribute definitions

• lt!ATTLIST Course Title CDATA REQUIRED
  Lect CDATA REQUIRED Lect2 CDATA
  IMPLIED Semester (firstsecond) first
• gt

44
Entities

• DTDs can also contain entity definitions
• Simplest use is to substitute in any parsed text
  (PCDATA) eg
• uos
• CDATA is not parsed, so entities will not be
  substituted

lt!ENTITY uos The University of
Sheffield gt
45
Alternative to DTDs XML Schema

• XML Schema is a proposal to introduce a grammar
  definining language which uses XML
• Adds better typing
• Predefined byte, float, long, time, date,
  boolean, binary, language, uri-reference,
• Boundaries on data values
• Pattern-matching

46
Overall summary

• Knowledge of XML is essential for all computer
  scientists
• Should lead to a better web with easier to find
  information
• Interoperability
• Impetus towards robust and open standards within
  industry sectors
• Supports internationalisation via UNICODE
• Hardly ever need to write a parser again!

47
Online documents

• XML Tutorials for Programmers
• http//www-106.ibm.com/developerworks/education/t
  utorial-prog/abstract.html
• (online XML parser -- requires registration)
• Transforming XML to PDF
• http//www-106.ibm.com/developerworks/education/tr
  ansforming-xml/xmltopdf
• Why XML?
• http//www.w3.org/XML/1999/XML-in-10-points
• XSL for fun and diversion
• http//www-106.ibm.com/developerworks/library/hand
  s-on-xsl/
• Simplify XML programming with JDOM
• http//www-106.ibm.com/developerworks/java/library
  /j-jdom/
• Easy Java/XML integration with JDOM, Part 1
• http//www.javaworld.com/jw-05-2000/jw-0518-jdom.h
  tml
• Tip Using JDOM and XSLT
• http//www-106.ibm.com/developerworks/java/library
  /x-tipjdom.html

48
Websites

• http//www.xml.org
• http//www.jdom.org
• Special thanks to Professor Martin Cooke,
  m.cooke_at_dcs.shef.ac.uk for the primary creation
  of these slides and their content.