RE: [xsl] bad programming for speedup?

["Michael Kay" <mike@xxxxxxxxxxxx>]

In trying to reverse-engineer your code, it looks to me as if you are doing
a classic "group-adjacent" problem, where a group of adjacent row elements
are wrapped in a table element. In XSLT 2.0 the most efficient way to do
this should be <xsl:for-each-group group-adjacent="boolean(self::row)">. In
1.0 the most efficient would probably be sibling-recursion, but that's quite
hard work to code if you're not used to recursive programming. On the other
hand there are solutions in 1.0 that are easier to code, but which are very
inefficient if the number of siblings is large (typically O(n^2)).

So we need to see whether your "good" code really was good or not!

As for the question:

> Is it allowed to discard the rules of good programming for speed-up
desires?

it is of course as old as the hills, and is not specific to XSLT. The answer
is that only you know the requirements of the project well-enough to decide
the trade-offs between performance, portability, and maintenance cost. But
most experienced software engineers (I think) will tell you that when you do
this, you usually get a short-term advantage that proves expensive in the
long term.

The key point I think is that it's usually not necessary. In the vast
majority of cases there is a way of solving the performance problems that
doesn't require you to write bad code.

Michael Kay
http://www.saxonica.com/
 

> -----Original Message-----
> From: christoph.naber@xxxxxxxxxxxxxxxxxxx 
> [mailto:christoph.naber@xxxxxxxxxxxxxxxxxxx] 
> Sent: 24 July 2007 11:02
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: [xsl] bad programming for speedup?
> 
> Hello everybody,
> 
> I'm new to this list, so let me introduce myself: 
> My name is Christoph Naber. I come from Germany and work with 
> XML/XSL for about 2 years now.
> 
> I'd be pleased to hear your opinion about a stylesheet I've written.
> 
> The aim is to surround occurences of <row> - tags with a 
> <table> - tag. 
> I've done this with "good" XSL, what appears to be real slow, 
> and with a "bad" version, which inserts tags as <xsl:text>.
> 
> The second version:
> <xsl:template match="row" >
>         <xsl:if test="name(preceding-sibling::*[1]) != 'row'">
>                 <xsl:text
> disable-output-escaping="yes"><![CDATA[<table>]]></xsl:text>
>         </xsl:if>
>         <xsl:text>
> </xsl:text>
>         <xsl:copy>
>                 <xsl:copy-of select="@*" />
>                 <xsl:apply-templates select="*" /> 
>         </xsl:copy>
>  
>         <xsl:if test="name(following-sibling::*[1]) != 'row'">
>                 <xsl:text
> disable-output-escaping="yes"><![CDATA[</table>]]></xsl:text>
>         </xsl:if>
> </xsl:template>
> 
> 
> This solution is much faster, but it makes use of bad XSL programming.
> 
> What are you thinking, is it allowed to discard the rules of good 
> programming for speed-up desires?
> 
> Christoph Naber
> 
> 
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