Showing posts with label XSL/XML. Show all posts
Showing posts with label XSL/XML. Show all posts

Friday 5 April 2013

What is CDATA , PCDATA in XML and where these should be used?



PCDATA - Parsed Character Data
XML parsers normally parse all the text in an XML document.
When an XML element is parsed, the text between the XML tags is also parsed:
<message>This text is also parsed</message>
The parser does this because XML elements can contain other elements, as in this example, where the <name> element contains two other elements (first and last):
<name><first>Bill</first><last>Gates</last></name>
and the parser will break it up into sub-elements like this:
<name>
  <first>Bill</first>
  <last>Gates</last>
</name>
Parsed Character Data (PCDATA) is a term used about text data that will be parsed by the XML parser.

CDATA - (Unparsed) Character Data
The term CDATA is used about text data that should not be parsed by the XML parser.
Characters like "<" and "&" are illegal in XML elements.
"<" will generate an error because the parser interprets it as the start of a new element.
"&" will generate an error because the parser interprets it as the start of an character entity.
Some text, like JavaScript code, contains a lot of "<" or "&" characters. To avoid errors script code can be defined as CDATA.
Everything inside a CDATA section is ignored by the parser.
A CDATA section starts with "<![CDATA[" and ends with "]]>":
<script>
<![CDATA[
function matchwo(a,b)
{
if (a < b && a < 0) then
  {
  return 1;
  }
else
  {
  return 0;
  }
}
]]>
</script>
In the example above, everything inside the CDATA section is ignored by the parser.


Notes on CDATA sections:
A CDATA section cannot contain the string "]]>". Nested CDATA sections are not allowed.
The "]]>" that marks the end of the CDATA section cannot contain spaces or line breaks.