2个Xpath表达式之间的区别

Question

What's the difference between these two Xpath expressions?

$z!="actors"
and
not($z="actors")

Thanks a lot!

Answer 1

This is spelled out in detail in the XPath specification :

NOTE : If $x is bound to a node-set, then $x="foo" does not mean the same as not($x!="foo") : the former is true if and only if some node in $x has the string-value foo ; the latter is true if and only if all nodes in $x have the string-value foo .

Essentially, all the general comparison operators = , != , < , <= , > and >= are implicitly existentially quantified over their arguments - X op Y is true if there is any pair of values from X and Y that satisfies the condition.

$z != "actors"

means there is a node in $z that has a value other than "actors" (and there may also be other nodes in $z that do have the value "actors", the test will still be true if any of them have a different value), whereas

not($z = "actors")

means it is not the case that there is a node in $z whose value is "actors".