Re: [Fenfire-dev] PEG swamp_easier--benja: An easier API for Swamp

[Benja Fallenstein]

Tuomas Lukka wrote:
> On Mon, Sep 22, 2003 at 02:29:49PM +0300, Benja Fallenstein wrote:
>
> > Tuomas Lukka wrote:
> >
> > > Why *should* it work for "equivalent" triples?
> >
> > Because the same thing can have more than one name (node in the graph), 
> > and if e.g. "c = d," then the triple "a b c" entails "a b d." Not 
> > allowing "a b d" to be in a graph at the same time as "a b c" is like a 
> > calculator that can compute 7+3+2, but not 7+3+0+2.
>
> As long as the definition of equivalence is as fuzzy as you have made
> out, 

I haven't made it fuzzy at all. There is a set of resources; there is a 
set of names for these resources, and a resource can have more than one 
name (or no name at all). Two triples of *names* of resources (i.e., 
nodes) are equivalent if the subjects name the same resource, the 
predicates name the same resource, and the objects name the same 
resource. If you see any fuzziness there, I suggest you get a little 
clearer.

Also, I'm not making any definitions, I'm just trying to explain. If you 
want to have a look at the sources, see for example 
http://www.w3.org/TR/owl-ref/#IndividualIdentity .

> I think it's fine: I see it more like 7+3+2 != 7+3+2+epsilon  

I don't see any relation between this and the issue at hand.

> If someone wants equivalences to work, what they can do is *unify* 
> the equivalent nodes of the graph **before** running code on it.

Knowing which names represent the same resource is not generally 
possible. You can know *some* equivalences, but not all. (E.g. if you 
have a property with cardinality 1, but more than one triple with that 
property and the same subject, then you know that all the objects are 
names for the same resource (or the graph states a contradiction). This 
is why returning an arbitrary one of the objects in ``getObject()`` 
should be fine-- they should all represent the same resource.)

- Benja