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Re: CDATA vs. Escaped characters

• To: xml-dev@l...
• Subject: Re: CDATA vs. Escaped characters
• From: Mike Brown <mike@s...>
• Date: Wed, 20 Mar 2002 17:58:29 -0700 (MST)
• Action:
• Cc: NBEYER@c...
• In-reply-to: <68ADFB4BE17A614B80FFFF6CDBC1A8160C6A79B2@m...>"from Beyer,Nathan at Mar 20, 2002 08:59:40 am"

Beyer,Nathan wrote:
> Are there any advantages, disadvantages or limitations in using CDATA
> sections as opposed to escaped character sequences? Or Vice Versa?

A couple of things I can think of offhand:

1. CDATA sections cannot contain "]]>" (the sequence that marks the end of the
CDATA section). If you can't guarantee that your data won't contain that
sequence, it might be more trouble than it's worth to make the necessary
workarounds.

2. Consider parsing differences and the effect on memory:

Using <doc>foo<![CDATA[bar]]>baz</doc>, the DOM gives you 3 children of
element 'doc' ...or in SAX, 3 separate calls to characters():

% python
>>> from xml.dom.minidom import parseString
>>> d = parseString('<doc>foo<![CDATA[bar]]>baz</doc>')
>>> d.childNodes[0].childNodes
 [<DOM Text node "foo">, <DOM Text node "bar">, <DOM Text node "baz">]

And using <doc>foo&#98;&#97;&#114;baz</doc, you get 5 children:

>>> d = parseString('<doc>foo&#98;&#97;&#114;baz</doc>')
>>> d.childNodes[0].childNodes                          
 [<DOM Text node "foo">, <DOM Text node "b">, <DOM Text node "a">,
  <DOM Text node "r">, <DOM Text node "baz">]

So that's 5 nodes using escaped text, vs 3 when using a CDATA section.
Obviously the ratios will depend on your actual data; I'm just giving an 
example.

On xsl-list we often scold people who try to misuse CDATA sections with
disable-output-escaping, telling them that CDATA sections are purely lexical
and that evidence of the original document's 'physicality' never makes its way
across the parsing divide. This is not entirely true, as you can see, although
in the case of XSLT processing, the XPath/XSLT data model swallows up the
difference.

3. If human readability/editability is important, there are times when
having a few large CDATA sections can be quite helpful.

4. Simple byte counts might be an issue. Using a CDATA section can cut down 
the space required to store or transmit those portions of a document that 
would otherwise be riddled with numerous escaped characters. On the other 
hand, many small, unnecessary CDATA sections can add unnecessary bulk to the 
size of the document.

There are no easy answers. Just some food for thought. Personally, I wouldn't
mind seeing CDATA sections just go away.

   - Mike
____________________________________________________________________________
  mike j. brown                   |  xml/xslt: http://skew.org/xml/
  denver/boulder, colorado, usa   |  resume: http://skew.org/~mike/resume/
                                             ^ (yes, i am looking for work)

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    • From: "Beyer,Nathan" <NBEYER@c...>

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