XML 2

1
XML 2

• Document Type Definition
• 12/01/2004

2
Using a Document Model

• Correct syntax rules ? well-formed doc
• Add rules to XML document to enforce structure
• DTD document type definition
• XML schema
• Document model defines the vocabulary and grammar
  rules
• Docs that correctly follow the rules are said to
  be valid.

3
Document Model

• Define the elements your document can contain
• Define the order in which the elements appear
• Require that certain elements appear
• Define the allowed number of occurrences of a
  given element
• Define the type of data an element can contain
• Define child elements for a given element
• Define the attributes for each of your elements
• Assign constraints to the attribute values

4
Document Model

• Are not required by XML and may not be needed
• Critical If you wish to share your document with
  other people

5
Overview of DTD

• Internal DTD
• Provided as part of the document
• External DTD
• Provided as an external file
• Syntax and rules for defining the pieces of a DTD
  are the same

6
Element Declarations

• The DTD must declare all elements used in the
  document
• Element declaration
• lt!Element element_name (content model)gt
• lt?xml version 1.0 standaloneyes?gt
• lt!DOCTYPE email
• lt!ELEMENT email (PCDTA)gt
• gt
• ltemailgt
• This is my e-mail message
• lt/emailgt

7
Content Types for Elements

• Text
• lt!ELMENT invoice (PCDATA) gt
• Elements
• lt!ELMENT invoice (element_name) gt
• Mixed Content
• lt!ELEMENT invoice (PCDATA, element_name) gt
• Empty
• lt!ELMENT invoice empty gt
• Any
• lt!ELMENT invoice ANY gt
• See next page

8
Special Character Notation

• message?
• The element occurs no more than once
• message
• The element can occur zero or more times
• message
• The element must occur at least once
• (xyz)
• Or operator, must take on a value listed

9
Attribute Declarations

• Give you control over the values of attributes
• lt!ATTLIST element_name
• Attribute_name1 data_type default_value
• Attribute_name2 data_type default_value
• Default Values
• FIXED must match the value supplied
• REQUIRED value must be supplied
• IMPLIED optional

10
Data Types for Attributes

• CDATA character data
• ID Unique identifier
• Enumerated List list of all possible values
  (separated by the pipe char)
• See next page

11
External DTD

• Reference to an external file
• lt?xml version1.0 standaloneno ?gt
• lt!DOCTYPE emails SYSTEM emails.dtd gt
• lt!DOCTYPE emails SYSTEM http//www.acme.com/emails
  .dtd gt
• Syntax is exactly the same as before
• Public DTD
• lt!DOCTYPE emails PUBLIC //W3C//DTD XHTML 1.0
  STRICT//EN DTD/HTTP/www.w3c.org/DTD/xhtmll-stric
  t.dtdgt
• DTD for xhmtl.

12
XML Schemas

• An alternative to DTD that offers a more powerful
  way to describe XML components
• Allows you to match string patterns within the
  content
• Provides more data types
• Boolean, numbers, dates, times
• Allows you to define your own data type
• Supports namespaces

13
Creating the Presentation

• Separating the content allows you to change the
  presentation without changing the content
• You can use this method to format for different
  clients
• Use a different style sheet for each client

14
Cascading Style Sheets

• They work the same way in XML as HTML
• Contains rules that tell the browser how do
  display certain elements
• Style information resides in an external file
  that usually ends with .css
• See next page

15
Problems with CSS

• Not a programming language
• When displayed, elements must appear in the same
  order in which they appear in the XML document
• Cant perform mathematical computations
• Cant make logical decisions
• Doesnt support relationships between siblings

16
XSL Extensible Stylesheet Language

• Addresses the limitations of CSS
• XSL stylesheets will provide presentation options
  for a much wider range of output formats
  including voice and print
• Provides much greater control and flexibility
• Has a built in programming language
• Much harder to learn than CSS