XML

1
XML

• Extensible Markup Language
• 11/29/2004

2
What is XML?

• Not a markup language
• Set of tools used to create new markup languages
• Metalanguage
• Open standard
• Plain text file

3
Fundamentals of Markup Languages

• A set of rules that define the layout, format or
  structure of text within a document
• Apply markup instructions
• Document is formed (processed)
• SGML
• Tex
• HTML

4
HTML Limitations

• Elements are used primarily for defining
  presentation and formatting styles
• Has a limited number of elements
• Lacks flexibly and extensibility
• Searching the content of HTML documents produces
  poor results

5
Benefits of XML

• Allows the data to be self-describing, as opposed
  to being limited by a predefined set of elements
• You can provide rules for XML elements that limit
  the type of data than an element can contain
• Legs you create custom data structures for
  industry specific needs

6
Benefits of XML

• Because XML describes data, the data can be
  displayed in any number of ways by applying
  different presentation styles
• Can be used to interchange data between
  proprietary formats and between different
  databases
• Has robust and reliable data searching
  capabilities

7
Separating Data from Presentation

• XML elements are used to describe the data, not
  the format
• ltphone numgt245 5585lt/phone numgt
• Style sheet to describe now to display phone
  numbers

8
XML vs. HTML

• XML is not dependent on a single document type or
  set of markup elements, HTML is
• HTML specification defines a finite set of
  elements, XML allows you to define elements that
  best fit your document or data
• XML separates presentation from data

9
XML vs. HTML

• Browsers are fairly forgiving of HTML. XML is
  extremely strict about correct syntax
• HTML tags are not case-sensitive. XML is.
• HTML is web oriented. XML can be used for any
  kind of data

10
XHTML

• The best of both worlds
• Merges XML with HTML
• Allows a quick transition to XML syntax for
  existing HTML documents
• XHTML tags are all lower case
• All tags have a start and end tag

11
XML Example 1

• Difference between HTML and XML
• Expand/collapse
• Hierarchical structure
• Parent/child
• Nesting of elements
• Root Element
• Job-Posting
• Create a set of tags to define the data for a job
  posting

12
Components of XML Documents

• Declaration tells the browser it is a XML
  document
• lt?xml version1.0 ?gt
• XML elements
• Start tag ltelement namegt
• Content
• End tag lt/element namegt

13
XML Elements

• Root element topmost or outermost node
• Type of object you wish to represent
• Parent/child/sibling elements
• Empty elements
• ltbr /gt ltimg /gt ltp /gt

14
XML Attributes

• Pieces of information that help to describe or
  label XML elements
• Name-value pairs
• ltmovie sourcehttp//whatevergtlt/moviegt
• ltmoviegt
• ltsourcegthttp//whatever lt/sourcegt
• lt/moviegt
• Elements vs Attributes
• Use elements when the data contains children
• Attributes cannot have child elements
• When the data contain a large amount of text use
  elements

15
XML Entities

• Used as placeholders for content in an XML
  document
• General entities
• Character special characters
• Content common block of content
• Unparsed binary or other nontext data
• Parameter entities
• Cover later

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Character Entities

• lt?xml version1.0 ?gt
• ltequationgt 50 lt 100 lt/equationgt
• ltequationgt 50 lt 100 lt/equationgt
• Others
• -- apos
• -- quote
• gt -- gt

17
Content Entities

• Are defined within the internal subset of a DTD
  (document type definition)
• Are defined within a document after the XML
  declaration and before the start of the root
  element
• lt!ENTITY state New Yorkgt
• ltaddressgt
• ltstategt state lt/stategt
• lt/addressgt

18
External Entities

• Used when information will be used in multiple
  XML files
• See business.xml description.xml

19
Unparsed Entities

• Data that is not text
• lt!ENTITY picture SYSTEM sunset.gif NDATA GIFgt
• XML Comments
• lt!-- this is a comment --gt

20
Well Formed Documents

• XML document that adheres to XML syntax is said
  to be well formed
• All XML Documents must contain one and only one
  root element
• All elements must have a start and end tag
• Elements must be nested properly and cannot
  overlap
• All attributes must have a value and it must be
  enclosed in quotes

21
Well Formed Documents

• Attributes must be placed in the start tag
• No attribute can appear more than once
• Element names are case sensitive
• lttitlegt Well Formed Documents lt/TITLEgt
• Element names can start with letters or an
  underscore and can contain only letters, numbers,
  hyphens, periods and underscores

22
XML Parsers

• program that checks your XML document to ensure
  that your document is well formed
• Nonvalidating looks for syntax errors
• Validating checks your document against a DTD
  or schema
• Think of it as a complier