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   Re: Questions on DCD

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  • From: John Cowan <cowan@locke.ccil.org>
  • To: XML Dev <xml-dev@ic.ac.uk>
  • Date: Thu, 01 Oct 1998 13:05:50 -0400

Olivo Miotto wrote:

> 2) I can understand that compatibility with RDF is a noble target,
> but I think the interchangeability of Elements and Attributes (DCD
> section 2.1.2) clouds the water, making it more difficult to process
> DCD files. I would rather the syntax="explicit" form be the only way
> of specifying DCD. The remainder of my questions assume this
> form.

I agree.  As I have said repeatedly, RDF-compatibility means that
a format has to be processable by a naive RDF engine, not that
the application processing the format has to be able to handle
every possible RDF variation.

> 3) A philosophical question: has anyone drawn up a clear functional
> distinction between attributes and elements?

Much sweat has gone into the question of when to use attributes and
when to use elements in general.  No definitive answers exist.

> 4) Related to 3): DCD allows elements to also have default and
> fixed values like attributes. Am I correct in thinking that this is lost
> when producing a DTD from DCD?

> Related to this, it seems that there is little consistency between
> what is defined as an attribute and what is defined as an element. A
> good example is AttributeDef where, if Values is an element, then
> Default should also be, as it represents one of the above Values.

See above.
> 6) I know this is not going to make me popular, but I think that there
> are too many datatypes, and they mix storage and presentation
> formats. It seems to me that, in a text-based format, you should not
> have to care if an integer is i1, ui1 or whatever. Similarly, why have
> both char and string? And is there a real need for picture, scale and
> precision? Do we really need length for strings? Maybe I am not
> seeing the big picture here...

The idea is to be able to preserve the datatype limitations of the
source, so that an exact re-creation of it is possible from the
XML version.  I agree that the current version is a mess, though.

> 9) I don't really understand why we need ID-role when we have
> datatypes of id, idref and idrefs

Neither do I.
> 10) I'm not really sure what is meant by open/closed content. How is
> it different from ANY and Mixed content?

Open content has to be modeled in DTDs by ANY, but really means
"this is the desired content, but other elements are not erroneous".
SGML/XML DTDs can't express this.

John Cowan	http://www.ccil.org/~cowan		cowan@ccil.org
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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