[Xesam] abstract properties?

[Evgeny Egorochkin]

В сообщении от Thursday 14 February 2008 05:08:43 Jamie McCracken написал(а):
> On Thu, 2008-02-14 at 03:15 +0200, Evgeny Egorochkin wrote:
> > Hi guys,
> >
> > This is in response to the lengthy discussion on #xesam that happened
> > while I
> >
> > was sleeping:
> > >(22:35:51)  kamstrup:  in other words a field is abstract if and only if
> > > it
> >
> > has children
> >
> > >(22:36:17)  jamiemcc:  yes and is not used in searches
> > >(22:36:30)  kamstrup:  also meaning that third parties can not extend
> > > fields
> >
> > which does not have any children in the Xesam onto
> >
> > >(22:36:45)  kamstrup:  moreover I also think we agreed that you can not
> >
> > assign any value to an abstract field
> >
> > >(22:36:54)  kamstrup:  (maybe obvious)
> > >(22:36:57)  jamiemcc:  yes
> > >(22:37:12)  kamstrup:  good, I think we agree then
> > >(22:37:15)  jamiemcc:  abstract are like intermediate classes
> > >(22:37:22)  kamstrup:  yes
> > >(22:37:31)  jamiemcc:  they ar enot used directly but instead are always
> >
> > inherited from
> >
> > >(22:37:36)  kamstrup:  only leaf nodes of the onto can contain values
> >
> > The benefits of this approach:
> > >(22:54:46)  kamstrup:  and having this as a restriction in Xesam does
> > > not render us incompatible with Nepo
> >
> > This renders xesam incompatible with most if not any rdfs based
> > approaches. xesam->rdfs_derivative mapping is ok but it breaks in the
> > opposite direction.
>
> since when was full rdfs compatibility a necessity?

It's not a necessity, but a useful bonus for interoperability. Moreover I 
provided other reasons(specific functionality) that will break.

> xesam is supposed to be a subset of rdf (at least that was my
> understanding)
>
> If abstract fields are flawed then you need to demonstrate with suitable
> examples why.

Actually I demonstrated that abstract fields are an artifical limitation that 
doesn't help either implementation, performance or user-friendliness. This 
alone seems to be enough to drop this limitation for the sake of simplicity.

Specific examples where this already affects us is creator and relations 
hierarchy. The severity of problems this would create for people trying to 
extend the ontology is yet to be determined.

-- Evgeny