W3C home > Mailing lists > Public > public-rif-wg@w3.org > January 2007

Re: slotted notation -summary

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Tue, 09 Jan 2007 11:18:47 -0500
To: Christian de Sainte Marie <csma@ilog.fr>
Cc: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>
Message-ID: <19303.1168359527@cs.sunysb.edu>

> Michael Kifer wrote:
> > No, I said just the opposite! What you want is wrong.
> >
> > When I said "You want to map ..." you misunderstood me.
> > This expression was supposed to explain what you should really want, if you
> > saw the issue clearly.
> Oh, ok, I get it. Btw, I certainly do not claim to see the issue clearly 
> (which is why I try to get a clearer view :-).
> So, what you say is that we should do, if anything is:
> >>>
> >>>[...] to map the relational slotted notation to the OO slotted notation
> >>>- not the other way around. Relational slotted notation implies that object
> >>>Ids are inaccessible, while OO notation assumes that they are. So, you can
> >>>map OO to relational slots in a certain sense.
> I do not understand what you mean.
> Here is what I understood. It would help me if you pinpointed where I am 
> wrong:
> The relational slotted notation p(slot1->val1,...,slotn->valn) says that 
> the tuple (val1 ... valn) belongs to relation p, where val1 plays role 
> slot1 etc. The same expression, if it were in OO slotted notation, would 
> mean that object p has values vla1 to vlan in slots slot1 to slotn: so, 
> it certainly says that val1 to valn are related in the proper roles 
> (thus implying the relational notation);

I don't see where this "thus" comes from.

> it also says that the relation 
> is embodied in object p, which the relational notation does not say 

What does "relation is embodied in ..." mean?

Please understand me. I am not trying to trick you or anything like that.
You are using informal language intermixed with statements, which I
interpret logical arguments, so I am trying to understand your logic.

> (thus the relational notation does not imply the OO notation).

True. Neither implies the other. This was a point in my essay.

> If this is (or, maybe, if this were) correct, one could transform from 
> OO slotted notation to relational, but not the reverse. Hence my proposal.

No. You can't have a full semantics-preserving transformation from OO to
relational (provided that you have a sufficiently expressive language on
top of OO - Horn will do). But you can translate from relational to OO.
The price you will pay in this second case is convenience, but you won't
loose expressiveness.

> You tell me that it is wrong: can you help me understannd why?

I hope the above helps. The source of your confusion is in thinking that
relations are somehow embodied in objects.  In principle this is true:
relations can be represented as OO classes, and a class is an object.  But
your mental picture of this embodiment is wrong. At least, I don't
understand what it is; my claim that it is wrong is based on the
conclusions that you are reaching.


> Christian
Received on Tuesday, 9 January 2007 16:21:26 UTC

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