RE: [OEP] The n-ary relations draft is ready for outside review

Hi Natasha,

I enjoyed the n-ary relations draft[1].  I have only one substantive
comment. 

I think it is important to point out that in some (many?) cases,
instances used to represent n-ary relations *should* have distinguishing
names, and that using blank nodes instead is a potential design pitfall.


In section "Considerations when introducing a new class for a relation",
the first bullet points out:
[[
In our example, we did not give meaningful names to instances of
properties or to the classes used to represent instances of n-ary
relations, but merely label them _:Temperature_Observation_1,
Purchase_1, etc. In most cases, these individuals do not stand on their
own but merely function as auxiliaries to group together other objects.
Hence a distinguishing name serves no purpose.
]]

However, I think the Purchase example is an excellent illustration of a
case where the instance *should* have a distinguishing name, i.e., each
purchase should have its own URI so that other documents can refer
specifically to that purchase instance.  Later, when the buyer and
seller are discussing the transaction -- for example, if the order
wasn't received when expected -- then they can easily and unambiguously
refer to it.  If the instance does not have a distinguishing name, then
less convenient, direct and efficient means must be used to refer to it.

To summarize, my points are;

1. In some cases, instances used to represent n-ary relations *should*
have distinguishing names (URIs) -- not blank nodes.

2. The Purchase example is a good illustration of such a case.

3. Using blank nodes in such cases is a potential design pitfall.

Does this make sense, or have a misunderstood something?

Reference
1.
http://smi-web.stanford.edu/people/noy/nAryRelations/n-aryRelations-2nd-
WD.html

David Booth

Received on Thursday, 15 September 2005 15:47:49 UTC