Subject: Re: [xsl] Is it possible to store XSLT code fragments as data and then dynamically evaluate those code fragments? From: "Martin Honnen martin.honnen@xxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> Date: Thu, 20 Jun 2019 11:49:14 -0000 |
Hello XSLT experts!
As you know, XPath expressions can be stored in an XML document and then an
XSLT program can be written which inputs each expression and dynamically evaluates them. For example, I created several XPath expressions to query Book data; I stored the XPath expressions this way:
evaluates the expression against the Book document:
<Queries> <Query> <XPath>/Bookstore/Book</XPath> </Query> <Query> <XPath>/Bookstore/Book[Binding eq 'paperback']</XPath> </Query> </Queries>
Then I created an XSLT program which loops over each XPath expression and
/>
<xsl:variable name="queries" select="doc('XPath-Queries.xml')" />
<xsl:template match="/"> <Results> <xsl:variable name="book-doc" select="."/> <xsl:for-each select="$queries//Query"> <Query-Result> <xsl:variable name="result" as="element()*"> <xsl:evaluate xpath="./XPath" context-item="$book-doc"
them is terrific!</xsl:variable> <xsl:sequence select="$result" /> </Query-Result> </xsl:for-each> </Results> </xsl:template>
The ability to store XPath expressions as data and then dynamically evaluate
I would like to take the next step and store XSLT code fragments as data and
then dynamically evaluate them. For example, I have a code fragment for converting the cost of a Book in U.S. Dollars (USD) to the cost in Great Britain Pounds (GBP):
<Book currency="GBP"> <xsl:value-of select="number($book-in-usd/Cost) * 0.79" /> </Book>
I vaguely recall that long ago there was a proposal by the XSLT working
group to provide an eval() function which would do exactly what I desire; but I checked the latest specification and it appears the eval() function wasn't accepted. Bummer.
The big picture is this: I want to perform various mapping operations on the
Book data. I want the mapping operations expressed in a declarative manner so that Subject Matter Experts (SMEs) can review the mappings for correctness (e.g., upon reviewing the above code fragment the SME says: "Yes, that is the correct way to convert costs in USD to GBP"). Ideally, the mapping operations would be stored as data and then dynamically evaluated (after the SMEs have certified their correctness). What do you recommend? It appears that dynamic evaluation of XSLT code fragments is not possible, so what is the next best thing?
In XPath 3.1 there is the transform function to run an XSLT 3 stylesheet from XPath 3 or XSLT 3 or XQuery 3 code, it allows you to use apply-templates or call-template or even run one of your user-defined functions.
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