On 7/5/05, Frans Englich <frans(_dot_)englich(_at_)telia(_dot_)com> wrote:
Hi,
According to the XPath specifications are constructor functions and the cast
expression defined to be semantically equivalent. I wonder, why then provide
both?
Here my speculation:
* The two uses different default namespaces. Hence, it can be practical on the
stylesheet-writing level. But this aspect is not more than convenience,
right?
* A usability aspect of the language. One might argue that multiple ways of
expressing the same thing allows users to choose their way which fits them
the best(a psychological aspect). _For example_, the `cast as` expression can
be percepted as changing the type of an existing value, while a constructor
function can be percepted as creating a new value.
What was the reasoning for creating the two?
A "cast as" expression is a synonym for using a constructor function,
except in two cases, where a constructor function cannot be used:
- If the "?" must be used after the atomic type name to express that
an empty sequence is allowed.
- If there is no target namespace for the schema defining the type
(the type is in no namespace) -- in this case a constructor function
with no namespace prefix will bind to the default namespace of the
core functions (F & O).
BTW, this is the second question you ask, the perfect answer to which
can be easily found in Mike Kay's book "XPath 2.0 Programmer's
Reference" -- ISBN: 0-764-56910-4
Cheers,
Dimitre Novatchev
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