W3C home > Mailing lists > Public > public-qt-comments@w3.org > May 2003

[F&O] fn:type() proposal (Was: [XSLT 2.0] Is it possible to display the type of a node / value / variable?)

From: Jeni Tennison <jeni@jenitennison.com>
Date: Wed, 21 May 2003 18:35:20 +0100
Message-ID: <134-631635804.20030521183520@jenitennison.com>
To: public-qt-comments@w3.org

Michael Rys wrote:
> You can use the instance of and typeswitch expressions to inspect
> the type.
>
> Exposing the type name is a feature of the debugger in my opinion
> and not a language feature.

Currently you can't do useful things like:

  1. See if two nodes have the same type (which would be particularly
     useful if we want to enable users to create their own functions
     for testing node equality)
     
  2. Select all nodes of a particular type, where that type is
     specified via a parameter

  3. Perform a transformation that annotates every typed element with
     its type by adding an xsi:type attribute

These are the kinds of operations that XSLT users do quite commonly
with node *names*. It seems reasonable to assume that XSLT users will
want to do them with node types as well.

I can see fewer uses for a function that exposes the type of an atomic
value, but there are cases outside debugging. One use case would be
where you wanted to create an element wrapper around a particular
value and use xsi:type to indicate the type of the value held by the
new element.
     
So I propose a fn:type() function as follows:

---
fn:type($arg1 as item()?) as xs:QName*

If $arg1 is the empty sequence, fn:type() returns an empty sequence.

If $arg1 is an element or attribute node, fn:type() returns a sequence
of expanded-QNames. The first expanded-QName is the dm:type() of the
node, the second is that type's base type from the in-scope schema
definitions, the third is that type's base type and so on up the type
hierarchy. The last expanded-QName in the sequence is xs:anySimpleType
for an attribute node and xs:anyType for an element node.

If $arg1 is a text node, fn:type() returns the expanded-QName
xdt:untypedAtomic.

If $arg1 is any other kind of node, fn:type() returns an empty
sequence.

If $arg1 is an atomic value, fn:type() returns a sequence of
expanded-QNames. The first expanded-QName is the type of the atomic
value, the second is that type's base type from the in-scope schema
definitions, the third is that type's base type and so on up the type
hierarchy. The last expanded-QName in the sequence is
xdt:anyAtomicType.
---

Cheers,

Jeni

---
Jeni Tennison
http://www.jenitennison.com/
Received on Wednesday, 21 May 2003 13:35:26 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Tuesday, 27 March 2012 18:14:24 GMT