Re: CDATA sections in W3C XML Infoset

[John Cowan <jcowan@reutershealth.com>]

Bob Kline wrote:


> No?  We have quite a bit of code in our XML repository which uses XML
> commands over sockets for its client-server interface to the rest of the
> world.  Most of the commands embed an XML document being stored in or
> retrieved from the repository.  The embedded documents are wrapped in
> CDATA sections.

And when the embedded document already contains a CDATA section?  Bzzzzt,
not well-formed.

>  The logic for extracting a document from an incoming
> client command is essentially:
> 
>    Find the element containing the CDATA section.
>    Find the CDATA child of the element.
>    Hand the value of the CDATA section to the parser.

I admit this is an easy DOM-based hack.  But it shouldn't be
*that* much harder to know what element you are looking for,
pull out a Text child (initially there should be only one,
or you can normalize), and do the conversion below.

> Before you even think about suggesting how easy it would be to restore
> the angle brackets in the embedded document, let me point out that the
> < and > which are not delimiters for the element tags in the
> embedded document cannot be "restored" to < and >, and I submit that it
> is impossible in some cases to distinguish which those were.  Therefore
> information has been lost.

Not so if you encode properly.  By changing every "&" in the embedded
document to "&amp;" and every "<" to "&lt;" (conceptually in that order),
you get this result:

	Original	Embedding
	<		&lt;
	&		&amp;
	&lt;		&amp;lt;
	&amp;		&amp;amp;
	&amp;lt;	&amp;amp;lt

Etc. etc.  No information is lost: change every "&lt;" to "<" and
every "&amp;" to "&" (conceptually in that order) and the exact
original is restored.  In this encoding, ">" characters need not
be changed.

> Before you suggest that the embedded document should not have been
> wrapped in a CDATA section in the first place, let me say that:

[points snipped]

These points basically say that your embedded documents are text,
not necessarily XML.  The safe way to encode text in an XML document
is to use the mapping above.

-- 
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