Not that I'm picking on you specifically Wendell, but your reply was the
most blatantly representative of a class of responses of a particularly
XSL purist/snobbish nature which I find extremely objectionable. There
was a reply from a Mitch Amiano which actually supplied a suggested
approach which "appeared" entirely reasonable, so tried it out. I've
included the core XSL for both approaches below: the "bad" code which
had the 'disable-output-escaping' clause and the "good" code which
generated the Page element directly. Following are my performance
numbers on a test input file which had 22,004 Row elements and was
13,425,501 bytes large (the time output is from the Unix time(1)
command):
For the "good" (XSLT-correct) approach:
real 2:41:32.6
user 2:31:57.0
sys 1.9
For the "bad" (d-o-e) approach:
real 1:38.4
user 1:31.8
sys 1.0
The "good" approach took hours; the "bad" approach took minutes. For
those that will care, the test environment was a Sun Solaris platform
using the interim release of the Xalan C++ 1.4 XSLT processor.
I'm just curious, do those of you with this hard-line "purist" attitude
actually use XSL to do real work or are you mostly academics and tool
developers/vendors? I understand staying true to a paradigm up to a
point, but sooner or later "the rubber has to hit the road".
Regards,
Ed Knoll
p.s. This is not all of the XSL, just the differences.
---- "Good" XSL ------------------------------
<xsl:variable name='PageFirstRows'
select='/gnsl:Results/gnsl:Table/gnsl:Row[
(position() mod $RowsPerPage) =
1]' />
<xsl:template match="gnsl:Table">
<xsl:copy>
<xsl:copy-of select="@*" />
<xsl:apply-templates select="gnsl:Columns" />
<xsl:choose>
<xsl:when test="gnsl:Row">
<xsl:apply-templates select='$PageFirstRows' />
</xsl:when>
<xsl:otherwise>
<xsl:element name='Page' />
</xsl:otherwise>
</xsl:choose>
</xsl:copy>
</xsl:template>
<xsl:template match="gnsl:Row">
<xsl:element name="Page">
<xsl:for-each
select='.|following-sibling::gnsl:Row[$RowsPerPage >
position()]'>
<xsl:call-template name='CopyAll' />
</xsl:for-each>
</xsl:element>
---- "Bad" XSL ------------------------------
<xsl:template match="gnsl:Table">
<xsl:copy>
<xsl:copy-of select="@*" />
<xsl:apply-templates select="gnsl:Columns" />
<xsl:choose>
<xsl:when test="gnsl:Row">
<xsl:apply-templates select="gnsl:Row" />
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="$LineBreak" />
<xsl:text
disable-output-escaping="yes"><Page/></xsl:text>
<xsl:value-of select="$LineBreak" />
</xsl:otherwise>
</xsl:choose>
</xsl:copy>
</xsl:template>
<xsl:template match="gnsl:Row">
<xsl:if test="(position() mod $RowsPerPage) = 1">
<xsl:if test="position() != 1">
<xsl:value-of select="$LineBreak" />
<xsl:text
disable-output-escaping="yes"></Page></xsl:text>
<xsl:value-of select="$LineBreak" />
</xsl:if>
<xsl:value-of select="$LineBreak" />
<xsl:text disable-output-escaping="yes"><Page></xsl:text>
<xsl:value-of select="$LineBreak" />
</xsl:if>
<xsl:call-template name="CopyAll" />
<xsl:if test="position() = last()">
<xsl:value-of select="$LineBreak" />
<xsl:text disable-output-escaping="yes"></Page></xsl:text>
<xsl:value-of select="$LineBreak" />
</xsl:if>
</xsl:template>
Hey Mitch,
The horribleness of disable-output-escaping is not (to my mind) really an
issue of the well-formedness constraint either in the stylesheet or in the
output -- that's something of a red herring (though it is a risk and a sign
of the deeper problem). Rather, it's the violation of XSLT's processing
model, in which the transformation of the node tree and the
post-transformation serialization are clearly distinguished and kept
separate by design. *Any* solution that works by writing markup to output
using d-o-e creates a dependency on the serialization step. While this may
be acceptable in certain circumstances (e.g. writing SGML entity references
to output that are not otherwise provided for, when you *know* you're going
to write a file), it's horrible at other times, if only because the
designer has created this dependency unwittingly, and thus doesn't
understand why the transform breaks in a conformant architecture, like
Mozilla or transformation chains in Cocoon, where no file is getting
serialized.
The relevance of grouping is only that the "write markup" approach is
usually resorted to by newer XSLT programmers who don't know how else to do
grouping, and who fall back on their Perl or Javascript experience (or just
sheer ingenuity) to suppose that writing markup is the best or only
solution to the problem (it is neither).
I doubt that any experienced XSLTer would have a problem with either of the
solutions you offered (or Dimitre's, or Tom's), since none of them
introduce the dependency on serialization that is the problem with
d-o-e-based techniques for "outputting open/close tags independently".
There the distinctions are much more of coding style and performance; but
none of them use a technique that is prone to break the minute you move
your stylesheet into a different environment.
Cheers,
Wendell
--
Edward L. Knoll Phone (work) : (719)484-2717
e-mail (work) :
ed(_dot_)knoll(_at_)cosd(_dot_)fedex(_dot_)com
e-mail (business): eknoll(_at_)sf-inc(_dot_)com
e-mail (personal): edward(_at_)elknoll(_dot_)com
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