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Message from discussion It seems that XPath does not distinguish between an inexistent path and a null string?
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Peter Flynn  
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 More options Jun 27 2012, 3:54 pm
Newsgroups: comp.text.xml
From: Peter Flynn <pe...@silmaril.ie>
Date: Wed, 27 Jun 2012 20:54:50 +0100
Local: Wed, Jun 27 2012 3:54 pm
Subject: Re: It seems that XPath does not distinguish between an inexistent path and a null string?
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On 14/06/12 11:04, Alain Ketterlin wrote:

> "japisoft" <cont...@japisoft.com> writes:

>> When your document is parsed, the final result has no difference. But
>> from the schema/DTD view, there's a
>> difference because

>> <!ELEMENT somework EMPTY>

>> and

>> <!ELEMENT somework (#PCDATA)>

>> are not equal, so write :

>> <someword></someword>

>> is equal to

>> <someword/>

>> is only true if the content type is (#PCDATA) or

> Do you have a source for this claim?

It's been a long time, but I think you'll find the discussion in the
archives of the XML SIG at the time. I seem to remember we did it to
death and the consensus was that XML should not distinguish between the
two forms.

> I think it's wrong. (Not the fact
> that #PCDATA and EMPTY are different, the fact that there is a
> difference between the two forms of empty elements.)

Officially there is no difference. In practice, if your parser has
access to a DTD or Schema, it would be possible for it to detect if
content was allowed or not.

> The XML recommandation says: "If an element is empty, it must be
> represented either by a start-tag immediately followed by an end-tag or
> by an empty-element tag." (Section 3.1)

> The only difference I know of is mentioned in the next paragraph: "For
> interoperability, the empty-element tag must be used, and can only be
> used, for elements which are declared EMPTY." And "For interoperability"
> is defined earlier as non-binding.

It is still regarded as good practice in the publishing field, where the
semantics of potential mixed content can be important. It also serves as
a reminder to those who examine the markup that the element type cannot
have any content, rather than the current element just being empty by
chance.

///Peter


 
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