XML Overview

1
XML Overview

• XML is a cross-platform, software and hardware
  independent tool for transmitting information.

2
What is XML?

• Stands for Extensible Markup Language
• Much like HTML
• Designed to describe data
• Tags are not pre-defined
• Define your own
• Designed to be self-descriptive
• With a Document Type Definition (DTD) or XML
  Schema

3
XML vs. HTML

• XML is not a replacement for HTML
• Designed with different goals
• XML designed to describe data
• HTML designed to display data
• XML doesnt do anything
• Created to structure, store and send information
• Complement to HTML
• XML used to describe data, while HTML formats and
  displays the same data

4
Quick Examples

• ltnotegt
• lttogtRoselt/togt
• ltfromgtJacklt/fromgt
• ltheadinggtReminderlt/headinggt
• ltbodygtStay on the lifeboat!lt/bodygt
• lt/notegt

• User designs own tags and document structure
• No formatting information just meaning
• Another example
• http//www.upstateshakespearefestival.org/blog/rss
  /blog.php

5
How/Why to Use XML

• Separate data from HTML
• Store data in separate XML files
• Use HTML to format (possibly with data island)
• Exchange/share data among applications
• Many B2B applications
• Store data
• SQL versions for XML exist
• Make data more useful
• Plain text is hardware, software, application
  independent no proprietary DBMS issues

6
Syntax Notes

• Case sensitive
• Closing tags required
• Must have a root element
• ltrootgt
• ltchildgt
• ltsubchildgt.....lt/subchildgt
• lt/childgt
• lt/rootgt
• Elements and attributes (rules of thumb)

7
XML Validation

• A well-formed XML document has correct XML syntax
• A valid XML document conforms to a DTD or XML
  Schema
• Why validate?
• each of your XML files can carry a description of
  its own format with it.
• independent groups of people can agree to use a
  common DTD or schema for interchanging data.
• your application can use a standard DTD or schema
  to verify that the data you receive from the
  outside world is valid.
• you can use a DTD or schema to verify your own
  data.

8
DTD Example

• lt!DOCTYPE note
• lt!ELEMENT note (to,from,heading,body)gt
• lt!ELEMENT to (PCDATA)gt
• lt!ELEMENT from (PCDATA)gt
• lt!ELEMENT heading (PCDATA)gt
• lt!ELEMENT body (PCDATA)gt
• gt
• Interpretation
• May be internal or external to an XML file
• Likely to be abandoned for the W3C endorsed XML
  Schema

9
XML Schema Example

• XML-based alternative to DTD
• Richer and more powerful than DTDs
• lt?xml version"1.0"?gt
• ltxsschema xmlnsxshttp//www.w3.org/2001/XMLSch
  ema
• targetNamespace"http//www.w3schools.com"
  xmlns"http//www.w3schools.com"
  elementFormDefault"qualified"gt ltxselement
  name"note"gt
• ltxscomplexTypegt
• ltxssequencegt
• ltxselement name"to" type"xsstring"/gt
• ltxselement name"from"
  type"xsstring"/gt
• ltxselement name"heading"
  type"xsstring"/gt
• ltxselement name"body"
  type"xsstring"/gt
• lt/xssequencegt lt/xscomplexTypegt
  lt/xselementgt lt/xsschemagt

10
Displaying XML

• Examples no formatting
• http//www.w3schools.com/xml/cd_catalog.xml
• http//www.w3schools.com/xml/simple.xml
• Multiple RSS examples (with or without
  stylesheets)
• Recall no formatting information!

11
XSL

• You can format XML for display
• Extensible Stylesheet Language
• Family of recommendations for defining XML
  document transformations and presentation
• XSLT XSL Transformations
• XSLT is a programming language on its own
• Example
• XML
• XSLT (note looping structure)
• XML with XSLT

12
Data Islands

• An XML data island is XML data embedded into an
  HTML page
• Uses the ltxmlgt tag
• ltxml id"note" src"note.xml"gtlt/xmlgt
• Not visible until data island is bound to HTML
  elements

13
Data Island Example

• XML data http//www.w3schools.com/xml/cd_catalog.
  xml
• Data island and binding
• http//www.w3schools.com/xml/tryit.asp?filenamec
  d_catalog_island

14
Real World Applications

• RSS (Really Simple Syndication)
• AJAX

15
RSS(Really Simple Syndication)

• Distributable whats new for your site
• Mini database of headlines and descriptions
• Use XML to build a channel or feed
• Standardized links define RSS
• Contains static site info and dynamic info about
  news stories
• File must be validated

16
RSS

• Syndication
• Make list of links and/or content available on
  your site
• Make sure people know (use a link)
• Target to other web sites, news readers, e-mail,
  PDAs, cell phones, voice updates, etc.
• RSS Aggregators
• Most common use of RSS feeds
• Automatically gather RSS files from content
  providers and present them in a single place in a
  variety of formats
• Web portals (e.g., My Yahoo)
• E-mail clients (e.g., FeedBlitz)
• Standalone software (e.g., various newsreaders)

17
RSS

• Why make feeds available?
• Allow visitors to see whats new at your site
  without actually visiting
• Encourages more traffic
• Creating a feed
• Dont want to do manually!
• Many tools exist
• PHP includes an RSS library for generating feeds