Introduction to XML

1
Introduction to XML

• Allyson Falkner
• Spokane County ISD
• afalkner_at_spokanecounty.org

2
Overview

• Why XML?
• What is XML?
• Example XML document
• General rules of well-formed XML
• Parts of an XML document
• Applications for XML

3
Why XML?

• SGML (Standard Generalized Markup Language)
• an all encompassing markup language
• big and complex
• software to manage it is expensive.
• HTML (HyperText Markup Language)
• Simplistic
• no separation of style
• XML (eXtensible Markup Language)
• Flexibility of SGML
• Simplicity of HTML

4
What is XML?

• A set of rules to store and organize any
  information
• Open Standard developed by W3C (www.w3.org/TR/rec-
  xml)
• Unicode is its standard character set
• Separates content from style
• Very Structured

5
Example XML document

• lt?xml version1.0?gt
• ltmemo priorityimportantgt
• lttogtSaralt/togt
• ltsubjectgtReminderlt/subjectgt
• ltmessagegtDonapost forget, ltemphasizegtSWIGlt/emph
  asizegt tonight!
• ltgraphic filerefsmiley.face.pict/gtlt/messagegt
• ltfromgtAllysonlt/fromgt
• lt/memogt

6
General rules of well-formed XML

• must begin with the XML declaration
• must have one unique root element
• all start tags must match end-tags
• XML tags are case sensitive
• all elements must be closed
• all elements must be properly nested
• all attribute values must be quoted
• XML entities must be used for special characters

7
Parts of an XML document

• Document Prolog
• Elements
• Attributes
• Entities
• Others
• Comments
• CDATA
• Namespaces
• Processing Instruction

8
Document Prolog

• XML declaration
• Version
• Encoding
• standalone
• Document type declaration (root element type)
• Document type definition (DTD)
• Internal subset
• Entity declarations
• All or part of DTD

9
Elements

• Container element
• ltname att1val1 att2val2gt
• content
• lt/namegt
• Empty element
• ltname att1val1 att2val2/gt

10
Element Name

• Names can contain letters, numbers, and other
  characters
• Names must not start with a number or punctuation
  character
• Names must not start with the letters xml (or XML
  or Xml ..)
• Names cannot contain spaces

11
Element Content

• element content (elements only)
• simple content (text only)
• mixed content (both text and elements)
• empty content

12
Attributes

• namevalue
• Attribute name must be distinct within the
  element tag
• Cannot contain multiple values

13
Caution about Attributes

• Only data about data should be stored as
  attributes because
• attributes cannot contain multiple values (child
  elements can)
• attributes are not easily expandable (for future
  changes)
• attributes cannot describe structures (child
  elements can)
• attributes are more difficult to manipulate by
  program code
• attribute values are not easy to test against a
  DTD

14
Entities

• General entities
• name
• Character entities
• Predefined character entities (amp, apos, gt, lt,
  quote)
• Numbered character entities (231 or xe7 )
• Named character entities (must be predefined
  ISO-8879)
• Mixed Content entities
• Internal declared in doc prolog
• External in another file
• Unparsed entities
• lt!ENTITIY smiley SYSTEM /images/smile.gif NDATA
  GIFgt
• Parameter entities (used in DTDs)
• name

15
Others

• Comments
• lt! text and markup ?
• Cannot contain two dashes
• Cannot go before xml declaration
• CDATA (character data)
• lt! CDATA textgt
• Processing Instructions
• lt?name data?gt
• Namespaces
• No external DTD so difficult to use
• Cant validate

16
Applications for XML

• Communicating among applications over the web
• Storing databases
• Transforming data
• Repurposing data (display and use server
  different ways)
• Defining special data (math, music,graphics )
• Sharing data (news paper articles, )