Subject: [xsl] [XPath/XSLT 2:0] How to determine the type of an item ? From: Dimtre Novatchev <dnovatchev@xxxxxxxxx> Date: Sun, 2 Jan 2005 17:41:09 +1100 |
It is a common XSLT processing scenario that some intermediate results are produced and must be used later during the transformation. These results are typically stored within a node-set. Especially for a sequence of atomic values, there is no way of representing it "natively in XML" -- one has to wrapp every item in a node or contrive some other scheme such as coding the sequence as a pipe-delimited string. Things are even worse with a result, which is a node-identity (as opposed to a copy of a node)... To preserve this some kind of a key is necessary, such as one that matches a node using its generate-id(). Because as described the type of the result is generally lost when stored in such an intermediate structure, it is often difficult or impossible to use them correctly, when they are later reconstituted and used. For example, after such storage and re-activation an integer will become a string and this will affect how it is processed -- comparing it to another xs:integer with the value comparison operators will raise a type error, while using the general comparison operators will result either in a string comparison or in an integer comparison, depending on which operand is first. Certainly, this is not something new -- we know that XPath 2.0 made only the first step to a powerful enough type system. A simple way to overcome some of these difficulties will be a function, which given an item returns it type -- e.g. the string "xs:integer" Of course, ideally one would want a "type class" which captures the "signature" of a type, such as its constructor functions, its orderness (or lack of such), its "eq" and "gt" functions, its supertypes, etc. While this may be considerably difficult to provide in XPath 2.0, the simple function I described will suffice for many scenarios. My question: is it possible and how to implement this function. Cheers, Dimitre Novatchev.
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