RDF Specification: Ambiguity of the ABLOCK

Andrew Layman andrewl at microsoft.com
Thu Aug 7 00:54:41 BST 1997

--Andrew Layman
   AndrewL at microsoft.com

> -----Original Message-----
> From:	Andrew Layman 
> Sent:	Friday, August 01, 1997 4:55 PM
> To:	w3c-labels-wg at w3.org; w3c-dsig-collect at w3.org
> Subject:	RE: First draft of RDF specification for review
> The example shown in 5.1.4 shows an interesting aspect of RDF:
> <color>
>   <ablock>
>     <hue>1</hue>
>     <lightness>45</lightness>
>     <saturation>70</staturation>
>   </ablock>
> </color>
> Color is a property with three sub-elements. However, it is not
> written that way. Instead it is shown containing an ablock, which then
> has three sub-elements.
> What is the target of this ablock?  Section 5.1.1 implies that an
> ablock without an href has as its target the containing document.
> Here, the rule seems to be that the target is the immediate parent.
> Why do we need this ablock?  Why do we not just have a color that
> itself has three sub-elements, as in
> <color>
>   <hue>1</hue>
>   <lightness>45</lightness>
>   <saturation>70</staturation>
> </color>
> I think the reason we don't is that the RDF rule about properties is
> that they must be binary. That is, the target of the color property
> must be a single object. In actuality here, we have what amounts to a
> quaternary relation, so we have interposed this "ablock" element in
> order to reify the quaternary relation.
> I don't think this is the same kind of ablock at all as used in 5.1.1.
> In fact, I don't think that "ablock" is the right element. The literal
> interpretation of 5.1.4 is that the target of the color relation is a
> typeless thing with three properties. Should not the target be a
> color?  As in
> <color>
>     <colorHSV>
>         <hue>1</hue>
>         <lightness>45</lightness>
>         <saturation>70</staturation>
>     </colorHSV>
> </color> 
> We could also reach this conclusion by thinking about the colorHSV as
> a datatype describing how to interpret its subelements to produce a
> color. (This point has implications for general thinking about data
> types.)
> --Andrew Layman
>    AndrewL at microsoft.com
> -----Original Message-----
> From:	Ralph R. Swick [SMTP:swick at w3.org]
> Sent:	Friday, August 01, 1997 9:49 AM
> To:	w3c-labels-wg at w3.org; w3c-dsig-collect at w3.org
> Subject:	First draft of RDF specification for review
> The first draft of the Resource Description Framework Model and Syntax
> specification (Lassila & Swick, eds.) is now ready for your review and
> comment.
>   http://www.w3.org/Member/9708/WD-rdf-syntax-970801.html
> I would like to ask this working group's permission to distribute
> this draft to w3c-xml-sig.  xml-sig is the forum where technical
> discussions of XML are ocurring and they particularly need to see
> our requirements for the namespace tag.  The only reason I ask your
> consent is that while xml-sig is a W3C Members forum, it has quite
> a few non-Member invited experts.  I will distribute this draft to
> that list at 1600UTC on Monday, August 5 unless I hear serious
> objections before then.
> Thanks to all who have contributed thus far, and to each of you who
> will take the time to review and make suggestions for improvement.
> -Ralph and Ora

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