An Introduction to XML

1
An Introduction to XML
Paul Donohue
May 8th 2002 Hotel Senator Zürich
2
Overview
Topics we will cover

• What Is XML?
• Why Use XML?
• Defining Rules with XML
• Related Technologies
• Demonstration
• Summary
• Questions

3
What is XML?
XML In A Nutshell

• XML Extensible Markup Language
• Not a programming language
• An open standard for representing structured data
• Describes data structure and content
• Separates data from its presentation

4
What is XML?
Markup Clarifies Data

• A woman without her man is nothing
• A woman without her man, is nothing
• A woman without her, man is nothing

5
What is XML?
Some History
1969 Generalized Markup Language (GML)
1980 Standardized Generalized Markup Language (SGML)
1986 SGML becomes ISO standard
1991 Hypertext Markup Language (HTML)
1996 W3C begin work on a language to combine SGML HTML
1998 XML standard is published
6
What is XML?
An XML Document

• lt?xml version"1.0"?gt
• lttalk code"ID352"gt
• lt!--Example XML file--gt
• lttitlegtA PB / XML Messaging Systemlt/titlegt
• ltpresentergtMr Paul Donohuelt/presentergt
• ltaudiencegtPowerBuilder Developerslt/audiencegt
• lttimegt1330lt/timegt
• ltdategt2001-08-13lt/dategt
• lt/talkgt

7
What is XML?
Parts of an XML document

• XML Declaration

lt?xml version"1.0"?gt lt!DOCTYPE talk SYSTEM
DEMO.DTD"gt lttalk code"ID352" gt lt!--Example XML
file--gt lttitlegtA PB / XML Messaging
Systemlt/titlegt ltpresentergtMr Paul
Donohuelt/presentergt ltaudiencegtPowerBuilder
Developerslt/audiencegt lttimegt1330lt/timegt ltdategt200
1-08-13lt/dategt lt/talkgt

• Prolog

• Elements

• Attributes

• Comments

• Other Parts

8
What is XML?
Elements

• Elements are the basic building blocks of XML
• XMLs nouns
• Elements consist of start tag, contents and end
  tag ltanimalgtcatlt/animalgt
• Empty elements can be shown as ltanimal/gt
• Contents can be data or other elements
• Elements can own attributes

9
What is XML?
Attributes

• Attributes give further information about an
  element
• XMLs adjectives
• Attributes consist of name, equals and value
  cat_typepersian
• Attribute values are quote delimited strings
• Attributes are placed inside an elements start
  tag

10
What is XML?
Characters

• XML messages are text files
• XML is case sensitive
• XML uses the Unicode 2.1 character set
• Special codes for markup characters such as lt and
  

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What is XML?
Names

• All elements and attributes are named
• Must begin with a letter, underscore or colon
• Must continue with valid name characters
• Letter / Underscore / Colon
• Digit
• Hyphen
• Full stop
• May not begin with XML

12
What is XML?
XML vs HTML

• XML uses tags like in HTML
• XML complements HTML
• XML is for smart data
• XML is both data and document

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What is XML?
Data encoded as HTML

• lttable width"500" border"0" cellspacing"0"
  cellpadding"0"gt
• lttr bordercolor"FFFFFF" bgcolor"6666FF"gt
• lttd width"214"gtSybaselt/tdgt
• lttd width"150"gtltbgtPowerBuilder 7.1lt/bgtlt/tdgt
• lttd width"136"gtpound145.00lt/tdgt
• lt/trgt
• lt/tablegt

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What is XML?
Data encoded as XML

• ltSoftwaregt
• ltPublishergtSybaselt/Publishergt
• ltTitlegtPowerBuilder
• ltMajorVersiongt7lt/MajorVersiongt
  
• ltMinorVersiongt1lt/MinorVersiongt
• lt/Titlegt
• ltPrice currency"GBP"gt145.00lt/Pricegt
• lt/Softwaregt

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Why Use XML?
Six Good Reasons

• Royalty free
• Industry standard
• Platform vendor independent
• Self describing
• Flexible
• Caters for nested repeating data

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Why Use XML?
Royalty Free

• Nobody owns XML
• No software to purchase
• No licensing fees

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Why Use XML?
Industry Standard

• XML version 1.0 became a W3C standard in 1998
• Good support from vendors
• Low risk technology
• Large community of developers

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Why Use XML?
Platform Vendor Independent

• XML documents are text based
• Perfect for messaging
• There are no vendor-specific extensions
• PDA to Mainframe

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Why Use XML?
Self Describing

• Descriptive element attribute names
• The name / data combination is easy to understand
  ltpricegt11.50lt/pricegt ltcurrencygtGBPlt/currencygt
• XML can be viewed with a text editor

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Why Use XML?
Flexible

• XML can handle any structured data
• XML can be easily transformed
• Direct access to the required data

21
Why Use XML?
Nested Repeating Data

• Nested data
  An employee has an
  address and that address has a street and a post
  code
• Repeating data
  An invoice has one or
  more items on it
• Hard to do with traditional file formats

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Defining Rules
Well-Formed XML Documents

• Conform to the grammar of XML
• One root element
• Non-empty elements have start end tags
• Elements are nested correctly
• Attributes are not repeated within elements
• Attribute values are quoted
• Can be parsed by any parser
• The data may be nonsense

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Defining Rules
Valid XML Documents

• Must contain a valid document type declaration
• Must obey the constraints of that declaration
• Element sequence is valid
• Required attributes are provided
• Attribute values are a valid value
• Ensures data is valid for the application domain
• Rules are in a DTD or schema

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Defining Rules
Document Type Definitions (DTD)

• DTDs define validation rules for XML documents
• Elements contents, order occurrence
• Attributes valid default values
• DTDs are optional
• DTDs can be internal or external
• DTDs are written in XML Declaration Syntax

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Defining Rules
Schemas

• Schemas are more powerful that DTDs
• Data types
• Improved occurrence constraints
• Schemas are written in XML
• Schemas can refer to other schemas
• Get your DTD or schema correct before you code

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Defining Rules
Semantics

• Standard terms facilitate data exchange
• Industry-wide standards have emerged
• MathML Mathematical Markup Language
• CML Chemical Markup Language
• FPML Financial Products Markup Language
• CDF Channel Description Format
• Check if your industry or organisation has a
  standard

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Related Technologies
Overview

• Parsers SAX DOM
• Searching XPath
• Formatting CSS, XSL XSLT
• Linking XLink XPointer
• Resource Description Framework (RDF)

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Related Technologies
Simple API for XML (SAX)

• Event driven
• Can handle large files
• No random access
• Read only
• Primarily for Java

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Related Technologies
Document Object Model (DOM)

• Standard set of function calls
• XML loaded into memory
• Best for smaller files
• Data is parsed into a tree of nodes
• Language and platform neutral

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Demonstration
31
Summary
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Summary
What have we learnt?

• What XML is
• Why we should use XML
• How to define rules in XML
• XMLs related technologies

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Summary
Recommended reading
Title Professional XML Author Mark Birbeck et
al Publisher Wrox Press Inc ISBN 1861003110
34
Summary
Recommended reading
Title Fast Track To XML Author Eric
Zenor Publisher Sybase Article 1003388
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Summary
Useful Web Sites
XML Org www.xml.org   W3C www.w3.org/xml   XM
L FAQ www.ucc.ie/xml   XML Cover Pages
www.oasis-open.org/cover/sgml-xml   XML Journal
www.sys-con.com/xml
36
Summary
Useful XML Tools

• MS XML Notepad http//msdn.microso
  ft.com
• XML Spy
  http//www.xmlspy.com

37
Questions

• If you have any questions about this presentation
  please email me or visit my web site.
• Email info_at_pauldonohue.com
• Web www.pauldonohue.com