RE: semantic meaning of predicates

> Hi, I got one question regarding the semantic meaning of predicates.
> For example, in message:
> <a>
> 	<b>
> 		<id>1</id>
> 		<id>2</id>
> 	</b>
> 	<b>
> 		<id>3</id>
> 		<id>4</id>
> 	</b>
> </a>
> 
> 1. Is there a difference between (a)./a[b/id='1' and 
> b/id='2'] and (b)/a[b[id='1' and id='2']

Yes, there is a difference (though with this data, both give the same
answer). 

(a) means "select the <a> element if it has a <b> with an <id> of 1 and if
it also has a <b> with an <id> of 2".

(b) means "select the <a> element if it has a <b> that has both an <id> of 1
and an <id> of 2".

In other words, (a) will select the <a> element if the id="1" and id="2" are
on different <b> children, while (b) requires them to be on the same child.

Michael Kay