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Re: Proposed minor amendments to RDF 1.1 Semantics §5

From: Antoine Zimmermann <antoine.zimmermann@emse.fr>
Date: Thu, 27 Jul 2017 23:25:47 +0200
Message-ID: <597A5A5B.5070306@emse.fr>
To: Sam Kuper <sam.kuper@uclmail.net>, public-rdf-comments@w3.org
Dear Sam,


On 27/07/2017 19:00, Sam Kuper wrote:
> RDF 1.1 Semantics §5 says[1]:
>
> "IEXT(x), called the extension of x, is a set of pairs which identify
> the arguments for which the property is true, that is, a binary
> relational extension."
>
> I propose two small amendments to this sentence.
>
>
> # Proposed amendment 1
>
> s/pairs/ordered pairs/

In most mathematical writing, it is common to call a pair something that 
has a first element and a second element. So the pair (x,y) (or "< x, y 
 >" as written in the recommendation) is not the same as the pair (y,x) 
because the first elements are not the same. In other term, a pair is 
most often denoting an ordered pair. The notion of "ordered pair" is 
often used when it is important to distinguish it from an "unordered 
pair" which is in fact a set of two elements {a,b}. Similarly, an RDF 
triple (s,p,o) is an "ordered triple".

In any case, even if your notion of a pair differs from this one, the 
formal definition of IEXT is quite explicit about what it means because 
IEXT is a mapping "from IP into the powerset of IR x IR" and the notions 
of powerset and Cartesian product have very precise and well accepted 
meanings.

>
> Why? Suppose this triple is true, and is the entire graph:
>
> ex:a ex:x ex:b
>
> Also suppose that triple, which happens not to be part of the graph, is false:
>
> ex:b ex:x ex:a
>
>>From the first one, we could say, IEXT(ex:x) = {(ex:a,ex:b)}.
>
>>From this in turn, if (ex:a,ex:b) is not an ordered pair, then we
> could conclude that the following triple is true:
>
> ex:b ex:x ex:a
>
> However, it is not true (see above). So, we must consider (a,b) to be
> an ordered pair.
>
> If I am mistaken about this, I would be grateful for an explanation as
> to the nature of my error.
>
>
> # Proposed amendment 2
>
> s/property/property x/

The sentence in which this appears in the section is not a definition, 
it's simply explaining what IEXT is representing, in informal terms. I 
don't think we need to be overly precise in sentences that are merely 
explanatory. Especially since the document is already published as a 
recommendation, updates and errata should be made only for actual errors.

Your reading is correct and, at that point of the document, there is no 
other properties than x being mentioned, so there is no possible 
ambiguities, IMO.


Regards,
--AZ

> Why? Because the sentence should be explicit about which property it
> is referring to. My reading of the sentence is that x is a property,
> and x is also the property to which the sentence is referring, but I
> am not certain that my reading is correct. If it is, then the sentence
> should be amended as proposed in order to make it clear that that is
> indeed the correct reading.
>
> Equally, if my reading is wrong, then the sentence should be amended
> differently, in order to clarify the intended reading. (Do please let
> me know if my reading is wrong!)
>
>
> # Note and valediction
>
> If you reply to this email, please CC me, as I am not subscribed to
> this mailing list.
>
> Many thanks!
>
> [1] https://www.w3.org/TR/2014/REC-rdf11-mt-20140225/#simple-interpretations
>
Received on Thursday, 27 July 2017 21:26:13 UTC

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