Modifications to the skos:related property family to accommodate variations in thesaurus structure

*Doug, Ceri wrote:
> 
> 4. Not everyone considers Related (RTs) to be necessarily 
> symmetric (eg the AAT does not). Could 'symmetric' not be an 
> optional property of the relationship?
> 

I propose we change the comment of the skos:related property to indicate
that this property should NOT be considered as symmetric.

We then add an extension skos:relatedSymmetric (as a sub-prop of
skos:related) to be used in the case where related IS considered to be
symmetric.

*Doug, Ceri:
> 5. Is there any possibility of defining at least one subtype 
> of Related? Eg a Partitive (see below)?
> 
> 6. Good to have subtypes of the hierarchical relationships 
> but note that broader/narrowerPartitive is often restricted 
> to members of the same hierarchy (see Aitchison&Gilchrist). 
> In other cases, a Related relationship type is recommended.
> 

To accommodate the cases where the partitve relationship is treated as an
associative relationship (and NOT as hierarchical), I suggest we add two
extensions to SKOS-Core:

skos:relatedPartOf (sub-prop of skos:related)
skos:relatedHasPart (sub-prop of skos:related)

... So then users have the option to use either the hierarchical or
associative style properties to express the partitive relation, depending on
preference.

Al.