Introduction to XML

1
Introduction to XML

• The eXtensible Markup Language

2
HTML Vs. XML

• HTML is a markup language
• Fixed set of tags
• Tags describe fixed set of elements
• Covers formatting, semantics and structure
• ltbgt ltSTRONGgt ltTDgt
• XML is a meta-markup language
• No fixed set of tags all user defined
• Describes structure and semantics not
  formatting
• Formatting is done by use of style sheets
  stored in a separate file

3
XML Design Objectives

• W3C established 10 goals for XML
• Easily used on internet
• Must support wide variety of applications
• Compatible with SGML
• Easy to write programs that process XML document
• Minimal optional features (simplicity)
• Easy to understand by lay people
• XML design should prepared quickly
• Design of XML must be precise
• XML documents easy to create
• Terseness not important

4
Creating an XML document The Process
Create XML document
Parse document using XML processor
Display document
5
XML First Try

• lt?xml version1.0?gt
• ltGREETINGgt
• Hello, World
• lt/GREETINGgt

6
The XML Declaration

• lt?xml version1.0?gt
• The tag is xml and version is the attribute
• 1.0 is version of xml to which document conforms
• Always start with this declaration
• Note it is case-sensitive
• No white spaces allowed

7
The Element

• ltGREETINGgt
• Hello, World
• lt/GREETINGgt
• Above three lines form the GREETING element
• ltGREETINGgt - start tag
• Hello, World element content
• lt/GREETINGgt -end tag

8
Inserting Comments

• lt!--This is a comment which will not be
  displayed--gt
• ltGREETINGgt
• Hello, World
• lt!-- This is a test xml file --gt
• lt/GREETINGgt

9
CDATA Sections

• Used to display text as is without interpretation
• lt!CDATA
• Text to be entered
• gt
• may contain most markup characters (lt,gt,!, etc.)
• May be placed anywhere in the document
• Cannot be nested in another CDATA
• Cannot be empty

10
Example of CDATA section

• ltMESSAGEgt
• lt!CDATA
• This is a sample of how this tag others like it
  may be used
• gt
• ltMESSAGEgt

11
To show formatted elements

• To have the element content show with formatting,
  must do two things
• Create a stylesheet file
• Specifies how to interpret tags
• Add a processing instruction to the xml file.
• Tells the xml file to look at the stylesheet file
  for formatting instructions

12
Adding a stylesheet

• The interpretation of self-defined tags (like
  ltGREETINGgt) done through use of linked CSS or XSL
  file
• Create another file named GREETING.css
• Would be called GREETING.xsl for XSL file
• Define the formatting for the GREETING element
• GREETING display block font-size 16pt
  font-weight bold font-style italic color red

13
Processing Instruction

• lt?xml-stylesheet typetext/css
  hrefgreeting.css?gt
• Insert after the opening XML declaration
• Can use same CSS for multiple xml files
• Type is set to text/xml if using XSL
• Can also be linked to a URL

14
Structuring Data in XML

• Consider data about music
• Genres of music
• Hip Hop/Rap Alternative Blues Country Jazz
  Rock Latin World
• Singers
• Hip Hop/Rap
• Eminem Busta Rhymes Nelly Ja Rule Missy
  Elliot
• Album
• Busta Rhymes
• It Aint Safe No More
• Song
• It Aint Safe No More
• Make It Clap

15
Some of the tags

• You can make up your own names but they should
  be meaningful
• ltMUSICgt
• ltGENREgt
• ltARTISTgt
• ltALBUMgt
• ltSONGgt

16
Root Element

• Every good xml document has a root element
• Root elements contain all other elements
• In this case, the ltMUSICgt start tag is the first
  tag in the document
• lt/MUSICgt end tag will be the last
• Tags must be nested , never overlap

17
Nested vs Overlapping tags

• ltCONFERENCEgt
• ltTEAMgt
• ltPLAYERgt
• lt/PLAYERgt
• lt/TEAMgt
• lt/CONFERENCEgt

Example of NESTED TAGS
18
Nested vs Overlapping tags

• ltCONFERENCEgt
• ltTEAMgt
• ltPLAYERgt
• lt/TEAMgt
• lt/CONFERENCEgt
• lt/PLAYERgt

Example of OVERLAPPING TAGS