RE: [xsl] Testing for Missing or Empty Tags

[Wendell Piez <wapiez@xxxxxxxxxxxxxxxx>]

Hi Rechell,

At 01:42 PM 1/8/2004, you wrote:
> Thanks, Wendell, Vasu, Michael, and David for your helpfule responses.

You are very welcome.

> Am I correct that:
> 1)not(Tag[normalize-space()]) will treat all blanks as if it were empty
> text, whereas not(string(Tag)) will not?

Basically, but...

There's an important difference between

[a] Tag[normalize-space()] or Tag[string()]
    (short for child::Tag[normalize-space(self::node())] and
               child::Tag[string(self::node())] )

and

[b] string(Tag) or normalize-space(Tag)
    (short for string(child::Tag) or normalize-space(child::Tag) ) ...

The [a] expressions test true if there exists a Tag child with a non-null 
string value (string()) or a non-null normalized-string value 
(normalize-space()).

The [b] expressions perform the same tests, except only on the first Tag 
child of the context node: since the string() and normalize-space() 
functions require a single node as operand, the first node in the set in 
document order is used.

So, the answer is basically "yes", with the caveat that the two expressions 
are also not alike in that crucial other respect.

normalize-space() collapses white space and trims leading and trailing 
white space, so boolean(normalize-space('   ')) is false since 
normalize-space('   ') = ''.

> 2)If I had multiple sets of a given element, not(Tag[normalize-space()])
> will return true for the following xml document because of the second
> Tag element, while not(string(Tag)) will return false since the first
> tag element has text?
>
> <Xml>
> <Tag>somevalue</Tag>
> <Tag></Tag>
> <Tag>Another value</Tag>
> </Xml>

Not quite. Tag[normalize-space()] will test true by virtue of the existence 
of the first and third Tag elements (which have text content even when 
trimmed), so not(Tag[normalize-space()]) tests false.

You are correct, however, that not(string(Tag)) will test false since the 
first Tag child has text content besides whitespace.

If you wanted to test whether there exists a Tag child without text 
content, that would be test="Tag[not(normalize-space())]", which would test 
true in the above example because the second node passes the test in the 
predicate, therefore the node set returned is not empty.

Remember a node-set casts to Boolean "true" if there exists a node in the 
set, false if not.

I hope this helps--
Wendell



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Wendell Piez                            mailto:wapiez@xxxxxxxxxxxxxxxx
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