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Re: Best Practice: Element with data or element with childelem

  • From: Evan Lenz <evan@evanlenz.net>
  • To: David Carlisle <davidc@nag.co.uk>
  • Date: Mon, 21 Dec 2009 11:38:25 -0800

Re:  Best Practice: Element with data or element with childelem
I have to concur with David's critiques, but I think I can generalize 
the point you're trying to make: data-driven code is cool. The less your 
code has to know about individual names in the input data, the more 
general it can be.

However, in practice, I find that data-driven transformations are 
overrated. I'd rather design an XML structure that fits well with the 
data. For example, I'd want to use attributes when I know the value will 
only ever be text. And then I'd prefer clear, elegant code using a 
combination of generic rules ("data-driven", if you like) and rules 
using hard-coded names, especially as they make explicit my intentions.

Purely data-driven code is ugly boilerplate. I'd only make special XML 
design concessions for data-driven processing when the input contains a 
huge list of properties (such as when being dumped from a database).

Evan Lenz

David Carlisle wrote:
>> which approach is better, an image element that contains the location of a GIF file:
>>    <image>images/mighty_oj.gif</image>
>> Or, an image element that contains a child element, which contains the location of the GIF file:
>>     <image>
>>         <src>images/mighty_oj.gif</src>
>>     </image>
> At that level of generality, without knowing anything about the rest of
> the document these approaches are identical (just rename image to foo and
> src to image  in the second example). So it's impossible to make any
> comparison.
>> Likewise, which is better, a retailer
> Clearly that's just the same example with different element names.
>> Using the second approach all this information can be provided in the
>> XML document: 
> It can be provided somewhere in either solution.
>> The XSLT is not hardcoded to add a specific set of attributes;
> Of course it is! It has the hardcoded assumption that someone has gone
> to the trouble of designing an xml format with exactly the same
> attribute names as html but using elements rather than xml attributes. 
> I suppose it's possible someone has done that but unlikely.
> Far more likely is they just use the same attributes in which case you
> can just use <xsl:copy-of select="@*"/> or that the element names are
> different to the html attribute names in which case you need to encode
> a translation table in your conversion and "hardwire" specific names in
> the source and result document.
> In any case any features you can do with the second form you can clearly
> do with the equivalent 1st form, it just depends where the additional
> metadata is placed
> <imagedata>
>    <image>images/mighty_oj.gif</image>
>    <alt>...</alt>
> ...
> </imagedate>
> for example.
> David
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