XML and DOM

XML is the eXtensible Markup Language. It is designed to improve the functionality of the Web by providing more flexible and adaptable information identification. It is called extensible because it is not a fixed format like HTML (a single, predefined markup language). Instead, XML is actually a `metalanguage' -- a language for describing other languages -- which lets you design your own customized markup languages for limitless different types of documents. XML can do this because it's written in SGML, the international standard metalanguage for text markup systems.

XML documents conform to the following grammar:

XMLdocument ::= Pi* Element Pi*
Element     ::= Stag (char | Pi | Element)* Etag
Stag        ::= '<'  Name Atts '>'
Etag        ::= '</' Name '>'
Pi          ::= '<?' char* '?>'
Atts        ::= ( Name '=' String )*
String      ::= '"' char* '"'

XML consists of tags and text. Tags come in pairs <date>8/25/2001</date> and must be properly nested:

   <person> <name> ... </name> ... </person>              --- valid nesting
   <person> <name> ... </person> ... </name>              --- invalid nesting

    <title> The Big Sleep </title>
    <year> 1935 </ year>

<person>
  <name> Ramez Elmasri </name>
  <tel> (817) 272-2348 </tel>
  <email> elmasri@cse.uta.edu </email>
</person>

<addresses>
   <person> ... </person>
   <person> ... </person>
   <person> ... </person>
   ...
</addresses>

<author id="2787901">Philip A. Bernstein</author>

Please read XML in 10 points for more explanation.

The Document Object Model (DOM) is a platform- and language-neutral interface that allows programs and scripts to dynamically access and update the content, structure and style of XML documents. The following is part of the DOM Java interface:

public interface Node {
  public String             getNodeName();
  public NodeList           getChildNodes();
  public NamedNodeMap       getAttributes();
 ...
}
public interface Document extends Node {
  public NodeList           getElementsByTagName(String tagname);
  ...
}
public interface NodeList {
  public Node               item(int index);
  public int                getLength();
}
public interface NamedNodeMap {
  public Node               getNamedItem(String name);
  ...
}

  Parser parser = new Parser( "depts.xml" );
  Document doc = parser.readStream( new FileInputStream( "depts.xml" ));
  NodeList nodes =  doc.getDocumentElement.getChildNodes();
  for (int i=0; i<nodes.getLength(); i++)
  {   Node n = nodes.item(i);
      NodeList ndl = n.getChildNodes();
      for (int k=0; k<ndl.getLength(); k++)
      {   if ( (n.tagName = "dept") &&
               (((CharacterData) n.getFirstChild).getData = "cse") )
          {  Nodelist ncl = n.getElementsByTagName("tel");
             for (int j=0; j<ncl.getLength(); j++)
             {   nc = ncl.item(j); 	 	
                 System.out.print(((CharacterData) nc.getFirstChild).getData);
             }
          }
      }
  }