FW: content: sequence?

Andrew Layman andrewl at microsoft.com
Thu Aug 7 00:57:41 BST 1997

The following is a message to the RDF working group regarding sequence
in RDF.  This led to some subsequent discussion in which I argued that
if sequence is a generally useful concept, 3a is the best answer.  We
also discussed the relative merits of indicating sequence on the
containing element vs. the contained.

--Andrew Layman
   AndrewL at microsoft.com

> -----Original Message-----
> From:	Andrew Layman 
> Sent:	Monday, August 04, 1997 2:55 PM
> To:	w3c-labels-wg at w3.org; w3c-dsig-collect at w3.org
> Subject:	RE: content: sequence?
> We did not reach agreement on how best to handle sequence in Boston,
> though we did agree that there are times in RDF when sequence is
> significant and other times when it is not. We discussed the
> possibility of having an attribute on an element signalling to an
> application when it could ignore sequence. This was generally agreed
> to as a direction, but we did not agree on what the appropriate
> default should be.
> There were three approaches discussed:
> 1.	a.	Sequences are always important on some (tbd) elements
> (e.g. "list") and never on others.
> 	b.	Sequences are not important on some (tbd) elements (e.g.
> "ablock"), but are significant on all others.
> 2.	Sequence-significance could be indicated by an attribute,
> required on elements defined by RDF, and presumably unavailable on
> other elements. 
> 3.	Sequence-significance could be indicated by an attribute that
> can be used on any element. If omitted, and if no default was given in
> a schema, then 
> 		a.	The application should follow the XML precedent
> of treating sequence as significant (after all, it might be).
> 		b.	The application should treat sequence as
> insignificant (after all, that takes less processing).
> Separately, we briefly discussed whether sequence-significance should
> be lexically inherited, but this dissolved into the general difficulty
> of lexical inheritance.
> By my calculation, the only options fully compatible with XML without
> implying any sort of contextual processing or lexical inheritance are
> 1a, 2 and 3a.
> --Andrew Layman
>    AndrewL at microsoft.com
> -----Original Message-----
> From:	Tim Bray [SMTP:tbray at textuality.com]
> Sent:	Saturday, August 02, 1997 12:15 PM
> To:	w3c-labels-wg at w3.org; w3c-dsig-collect at w3.org
> Subject:	content: sequence?
> The draft does not, unless, I missed it, allow for sequence in the RDF
> model.  This is going to be widely required in all sorts of classes of
> metadata (examples on request).  I don't think RDF 1.0 is worthwhile
> without
> sequence.  
> Suggestion: RDF already has a list primitive.  If I say
> <list id="l001">
> <item>Panorama</item><item>Navigator</item><item>Notepad</item></list>
> <ablock href="http://...somewhere...">
>  <AppToOpenWith href="#l001" reftype="indirect">
>  </ablock>
> then I think we have a sequenced property value.  Does this work?
> Cheers, Tim Bray
> tbray at textuality.com http://www.textuality.com/ +1-604-708-9592

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