RE: The order of selected nodes in a select pattern with OrExpres sions?

[David Schach <davidsch@xxxxxxxxxxxxx>]

In XQL, upon which the Microsoft implementation of XSL patterns is based,
document order is preserved by unions.

> -----Original Message-----
> From:	Tyler Baker [SMTP:tyler@xxxxxxxxxxx]
> Sent:	Sunday, January 24, 1999 12:52 PM
> To:	xsl-list@xxxxxxxxxxxxxxxx
> Subject:	The order of selected nodes in a select pattern with
> OrExpressions?
> 
> One thing that does not seem to be clear in the XSL in the XSL draft is
> in what order the nodes should be selected in a select expression with
> or expressions present.
> 
> For example say I have an XML file:
> 
> <a>
>   <b1>
>     a
>   </b1>
>   <b2>
>     b
>   </b2>
>   <b3>
>     c
>   </b3>
> </a>
> 
> What if I have a template:
> 
> <xsl:template match=a>
>   <xsl:apply-templates select="b3 | b2 | b1">
> </xsl:template>
> 
> Should the output text be: cba, or should the output text be: abc.
> 
> A more general question is: "Is the order of the UnionExpressions more
> significant or is the document order of the elements more significant"?
> 
> Basically what I am getting at is should an XSL Processor evaluate each
> PathExpression in the UnionExpression separately and in the order that
> the UnionExpressions are in, or should an XSL Processor recursively
> evaluate each subtree expression of each path expression in the union
> expression in that order.
> 
> Right now I am under the assumption that an XSL Processor should do
> something like:
> 
> for each path expression in a union expression
>   select all nodes which match up with the last subtree expression of
> the currently tested path expression
> 
> Then filter out any repeatedly selected nodes in the list.
> 
> The spec only says that:
> 
> "The context of the right hand side expressions is the context of the
> left hand side expression. The results of the right hand side
> expressions are node sets. The result of the left hand side UnionExpr is
> the union of the results of the right hand side expressions."
> 
> My understanding here is that you select in the order in which the path
> expressions occur and filter out redundantly selected nodes.
> 
> Is this the right way to do things or am I barking up the wrong tree
> here?
> 
> Tyler
> 
> 
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