Question

This question is prompted by the rather militant refusal of developer Michael Rys to include the parsing of CDATA sections into FOR XML PATH because “There is no semantic difference in the data that you store.”

I have stored nuggets of HTML in CDATA nodes and other content that requires the use of special or awkward characters. However I don’t feel qualified to challenge Rys’s controversial assertion because, I suppose, technically he is correct in the scenarios where I’ve employed CDATA for convenience.

What’s really baking my noodle is that, as developers take to the internet begging for advice on how to render CDATA segments using FOR XML PATH, respondents continually direct them to use FOR XML EXPLICIT instead, the XML rendering method Rys cited as being the “query from hell”.

If we can really do without CDATA in every use case that anyone can suggest I guess we should stop moaning and reject CDATA usage henceforth. But if there are clearly defined cases where CDATA is essential Rys already undertook that he would bake it into FOR XML PATH going forward in the topmost link in this question.

So which is it to be? Are CDATA sections really relics of the past? Or should Rys pull his finger out and allow for CDATA parsing in FOR XML PATH? And while we’re at it, in the meanwhile, are there any hacks for getting FOR XML PATH to return CDATA sections?

Answer 1

CDATA sections are useful if you don’t care about the semantics of the data in them (i.e. you do not need to parse it – it is simply a run of characters), and you don’t wish to escape any of the XML within them.

The definition, according to w3:

CDATA sections may occur anywhere character data may occur; they are used to escape blocks of text containing characters which would otherwise be recognized as markup.

From wikipedia:

New authors of XML documents often misunderstand the purpose of a CDATA section, mistakenly believing that its purpose is to "protect" data from being treated as ordinary character data during processing. Some APIs for working with XML documents do offer options for independent access to CDATA sections, but such options exist above and beyond the normal requirements of XML processing systems, and still do not change the implicit meaning of the data. Character data is character data, regardless of whether it is expressed via a CDATA section or ordinary markup.

CDATA sections are useful for writing XML code as text data within an XML document. For example, if one wishes to typeset a book with XSL explaining the use of an XML application, the XML markup to appear in the book itself will be written in the source file in a CDATA section. However, a CDATA section cannot contain the string "]]>" and therefore it is not possible for a CDATA section to contain nested CDATA sections. The preferred approach to using CDATA sections for encoding text that contains the triad "]]>" is to use multiple CDATA sections by splitting each occurrence of the triad just before the ">". For example, to encode "]]>" one would write: