# Re: plural vs singular properties (a proposal)

From: Alan Ruttenberg <alanruttenberg@gmail.com>
Date: Mon, 23 Apr 2007 10:07:32 -0400
Message-Id: <6E4F9FFA-88BC-4E77-A944-BD4557453124@gmail.com>

To: Sandro Hawke <sandro@w3.org>
```
On Apr 22, 2007, at 8:47 PM, Sandro Hawke wrote:
> I keep running into a problem with modeling in RDFS/OWL where I don't
> know whether to use a multi-valued singular property or a single-
> valued
> plural (collection) property.

Hi Sandro,

This appears to me (correct me if I am wrong) to be a problem of
modeling in RDFS, not of modeling in OWL.  OWL's cardinality
constraints allow you to express that a property can have a single
value only (via "functional", or via explicit cardinality 1) or that
a property must be multi valued, for instance via mincardinality 2.

These properties can be applied globally or to specific individuals
(via using restrictions in the type of the individual). I can provide
examples, if that would be helpful.

Also, at least as far as OWL-DL goes, Style 2 is not an option.
However there is an lists-for-OWL approach that has been presented by
Nick Drummond et al, in e.g., http://protege.stanford.edu/conference/
2006/submissions/slides/7.1_Drummond.pdf. That would handle the
ordered case. The cardinality restrictions above handle the
"exhaustive" case.

If you agree with this analysis, then perhaps rather than introducing
a new term to RDFS to express this, the existing ones from OWL might
be reused.

Regards,
Alan

> For example:
>
> Style 1 - Singular Property
>
>     Turtle:   p:Charles f:child p:William, p:Harry.
>
>     N-Triples:
>               p:Charles f:child p:William .
>               p:Charles f:child p:Harry .
>
> Style 2 - Plural (Collection) Property
>
>     Turtle:   p:Charles f:children ( p:William p:Harry ).
>
>     N-Triples:
>               p:Charles f:children _:genid2 .
>               _:genid2 rdf:first p:William .
>               _:genid2 rdf:rest _:genid1 .
>               _:genid1 rdf:first p:Harry .
>               _:genid1 rdf:rest rdf:nil .
>
> I believe the dominant opinion is that one should use Style 1
> unless one
> needs one of the key features of Style 2, which are roughly:
>     a.  the values are ordered
>     b.  the values are exhaustive
>
> I've never liked having to make that tradeoff, and I think I now see a
> way to get out of it.
```
Received on Monday, 23 April 2007 14:05:57 UTC

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