Embedding Content as Element Content or As An Attribute Value

Marcus Carr mrc at allette.com.au
Sat Jan 10 04:02:51 GMT 1998

Michael Kay wrote:

> I think Marcus is wrong. The domain of application of SGML is different from
> the domain of application of XML, and the distinction between attributes and
> content which made sense in the SGML world is extremely perplexing to those
> with a background in data modelling and data structure design in other domains,
> who are legitimate members of the XML community.

I think you're making a few assumptions about how XML is going to be used - I
(and probably many others in the SGML community) have every intention of
re-badging SGML datasets as XML. The goal when designing an SGML dataset has
always been to create something application and system independent. The fact that
this can also be friendly to the web doesn't make me feel even a bit compromised.
I will take your word for it that this is all very perplexing to those with
different backgrounds, but those with their roots in SGML may also be "legitimate
members of the XML community".

> Philosophically - at least in terms of any ontological system I am aware of -
> it is a nonsense, and can be justified only in terms of pragmatic assumptions
> about information in the form of paper documents.

If you're suggesting that SGML is only for paper, you're not even close. We have
a number of sites where we have integrated databases with other sources and
dynamically generated HTML. We may prefer to generate XML, but that has no impact
on what format the source data takes.

> I will resign myself to accepting XML as it is, but to suggest that its
> deficiencies are there because SGML gurus decided ten years ago that they were
> a good thing is unhelpful and not particularly flattering to the SGML gurus,
> who designed it that way for a different purpose.

I don't think you read what I said. I didn't say that that anyone decided
anything was a good thing. In fact, what was being discussed has nothing to do
with the standard - there is no definitive correct approach, however you may find
the opinions of others who have faced similar situations useful.

> In the DTD I've been designing, for what it's worth, I'm currently using
> content for nearly everything, with very little use of attributes. The main
> reason is for future extensibility; elements can always acquire a richer
> internal structure, while attributes can't. The drawbacks (e.g. inability to
> specify any constraints on values, default values, etc) don't actually lose me
> much, because the constraints available for attributes are very limited anyway.

The above holds perfectly true for an XML or SGML DTD. Why is it so much more
relevant when you say it about XML than when someone might say it in an SGML


Marcus Carr                  email:  mrc at allette.com.au
Allette Systems (Australia)  email:  info at allette.com.au
Level 10, 91 York Street     www:    http://www.allette.com.au
Sydney 2000 NSW Australia    phone:  +61 2 9262 4777
                             fax:    +61 2 9262 4774

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