• eXtensible Markup Language



• W3C initiative led by Sun



• Next step in Web evolution



• Goes beyond the current limitations of HTML and CSS



• Will create new Web applications

• Web is not static -- has to evolve



• XML provides key features needed for a new generation of Web applications:
  
  
  • Extensibility
  
  
  
  • Structure
  
  
  
  • Validation
  
  
  
  • Late binding of presentation
  
  
  

• Microsoft is moving quickly to adopt and implement XML



• Netscape is late but trying hard to catch up



• Microsoft and Netscape agree that Web content will be managed using standards based on XML

XML is going to be an integral part of the Web.

• HTML is optimized for easy learning
  
  
  • One tag set for all applications
  
  
  
  • Predefined semantics for each tag
  
  
  
  • Predefined data structures
  
  
  
  • No formal validation
  
  
  



• HTML trades power for ease of use



• HTML is well suited to simple applications, but poorly suited to more demanding applications
  
  
  • Large or complex collections of data
  
  
  
  • Data that must be used in different ways
  
  
  
  • Data with a long life cycle
  
  
  
  • Data intended to drive Java applets or other programs
  
  
  

• No way to validate data structures or impose editorial control



• Difficult or impossible to reliably generate navigational aids



• Navigation usually has to be implemented by adding handcrafted hypertext links



• No concept of entity management (no mechanism for modular reuse)



• Context searching or other behavior based on semantic distinctions is difficult or impossible



• Cannot easily model data structures residing in databases

The next step is to learn about the XML DOM and XSLT.

If you want to learn about validating XML, the next step is learning about DTD and XML Schema.

The XML DOM defines a standard way for accessing and manipulating XML documents.

The XML DOM is platform and language independent and can be used by any programming language like Java, JavaScript, and VBScript.

XSLT is the style sheet language for XML files.

With XSLT you can transform XML documents into other formats, like XHTML.

The purpose of a DTD is to define what elements, attributes and entities is legal in an XML document.

With DTD, each of your XML files can carry a description of its own format with it.

DTD can be used to verify that the data you receive, and your own data, is valid.

XML Schema is an XML based alternative to DTD.

Unlike DTD, XML Schemas has support for datatypes, and XML Schema use XML Syntax.