Modeling question

[Jon Phipps]

Folks,

I'm looking for some community advice on how to best model this situation:

The RDA spec says that the rda:extent property applies to both
frbr:manifestation and frbr:item. Without getting into a discussion of
whether that's correct, I'm interested in the best way to model that.
It looks like there are at least a couple of options...

1) declare a single property with two domains:

<rda:extent> a rdf:Property ;
    rdfs:isDefinedBy <http://RDVocab.info/Elements> .
    rdfs:domain <frbr:Item> ,
                      <frbr:Manifestation> .

2) declare a single property with two subproperties:

<rda:extent> a rdf:Property ;
    rdfs:isDefinedBy <http://RDVocab.info/Elements> .

<rda:extentItem> a rdf:Property ;
    rdfs:subPropertyOf <rda:extent> ;
    rdfs:domain <frbr:Item> .

<rda:extentmanifestation> a rdf:Property ;
    rdfs:subPropertyOf <rda:extent> ;
    rdfs:domain <frbr:Manifestation> .

I think I prefer option 2 since it allows the base property to be
domain-free but still expresses the intent of the text and it's been
modeled this way elsewhere [1][2], but I'm wondering if anyone has a
good reason to prefer option 1? Or are there other ways of expressing
this that I haven't considered?

Cheers,
Jon Phipps

[1] http://RDVocab.info/Elements/identifierForTheItem
[2] http://RDVocab.info/Elements/identifierForTheManifestation