Re: Error in RDF 1.1 Concepts and Abstract Syntax

Dear Rachel,

sorry for a late answer, and thank you for point this out.

The definition is, indeed, a little confusing, but may be the problem is
not in step 6, but in the definition of D1 and D2:

> Two RDF datasets
<https://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#dfn-rdf-dataset>
(the RDF dataset D1 with default graph DG1 and any named graph NG1 and the
RDF dataset D2 with default graph DG2 and any named graph NG2)

This might be me being non-native, but I'm confused with "any named graph
NG1" in this sentence (and the same with NG2, of course). What does NG1
denote here? One particular named graph of D1? Each named graph of D1 (that
would be quite strange)? The set of all named graphs in D1?

Note that the last interpretation makes step 6 perfectly ok.

> <n, G> is in NG1 if and only if <M(n), M(G)> is in NG2

But then if would be worth rephrasing the definition of D1 as "the RDF
dataset D1 with default graph DG1 and **a set of named graphs** NG1)" (and
respectively for D2).

Otherwise, Ivan's proposal also makes sense: in step 6, replacing NG1 and
NG2 with D1 and D2 respectively

> <n, G> is in D1 if and only if <M(n), M(G)> is in D2

On Thu, 29 Aug 2019 at 18:05, Rachel Arnold <rlongley@vt.edu> wrote:

> Hi there,
>
> I am writing at the suggestion of Ivan Herman regarding an error in the
> definition of dataset isomorphism in
> https://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/#graph-isomorphism
>  .
>
> I include below an email correspondence that I have had with Ivan on
> August 28, 2019, including his proposed correction.
>
> Best,
> Rachel
>
>
> From Ivan:
> Rachel,
>
> I think you are right, the definition in item (6) seems to be erronuous.
>
> I believe the right formulation is something like
>
> 6. The named graph <n, G> is in D1 if an only if <M(n), M(G)> is D2
>
> Which is all right, because a named graph is defined (a few paragraph
> above) as "a pair consisting of an IRI or a blank node (the graph name),
> and an RDF graph".
>
> Your intuition is of course correct, but as this document does not define,
> or refers to, quads, your definition would not hold either...
>
> I would think that it is worth raising that erratum by sending a mail to
> public-rdf-comments@w3.org, so that, eventually, it would find its place
> in https://www.w3.org/2001/sw/wiki/RDF1.1_Errata. If, at some point, the
> RDF spec is reopened by a WG, this should be taken care of.
>
> Thanks!
>
> Cheers
>
> Ivan
>
> On 27 Aug 2019, at 22:48, Rachel Arnold <rlongley@vt.edu> wrote:
>
> Ivan,
>
> Thanks again for pointing me toward the document with the standard
> definition of dataset isomorphism. I have a question about the definition,
> specifically statement 6.
>
> There are a few things going on that are bothering me.
>
> - n is never properly defined. Is it a node? Blank node?
> - What does it mean for <n,G> to be *in* NG1? The opening statement of the
> definition says that NG1 is a named graph. It seems that 6 is treating NG1
> as if it is the collection of all named graphs.
>
> Here’s what I *think* statement 6 is intending to communicate:
>
> A triple t is in a named graph NG1 in D1 if and only if the triple M(t) is
> in NG2 in D2 where M(NG1) = NG2.
>
> Or perhaps more clearly:  <s,p,o,NG1> is in D1 if and only if
> <M(s),p,M(o),M(NG1)> is in D2.
>
> This makes me wonder - could statements 4 and 6 be replaced with
>
> <s,p,o,NG1> is in D1 if and only if <M(s),p,M(o),M(NG1)> is in D2.
>
> Or, maybe:
>
>  There is a one to one correspondence between NG1 in D1 and NG2 in D2 such
> that NG1 is RDF graph-isomorphic to NG2.
>
> I’d like to get this pinned down before I spend too much time translating
> my definitions into the standard, expected language.
>
> Thanks in advance for the help.
> Rachel
>
> --
>
> *Rachel F. Arnold, Ph.D.*
>
> Collegiate Assistant Professor and GTA Coordinator
> Department of Mathematics
> 540-231-8271 | 410 McBryde Hall
>
>
>
> ----
> Ivan Herman, W3C
> Home: http://www.w3.org/People/Ivan/
> mobile: +31-641044153
> ORCID ID: https://orcid.org/0000-0003-0782-2704
>
>
>
> --
>
> *Rachel F. Arnold, Ph.D.*
>
> Collegiate Assistant Professor and GTA Coordinator
> Department of Mathematics
> 540-231-8271 | 410 McBryde Hall
>
>