Re: RDF 1.1 Primer

On Nov 25, 2013, at 4:37 AM, Yves Raimond <yves.raimond@bbc.co.uk> wrote:

> Hello Pat,
> 
> First of all, many thanks for the comments - we'll go through them in
> more details in the coming days. I just had one question about the
> following:
> 
> [snip]
> 
> 
>> "We can then make statements about these two graphs, for example adding license and provenance information:
>> 
>>        <http://example.com/bob> <is published by> <http://example.org>.
>>        <http://example.com/bob> <has license> <http://creativecommons.org/licenses/by/3.0/>."
>> 
>> <hair tearing> AAAARRRRGGGH</hair tearing> NO WE CAN'T. Or at least, this use is NOT SUPPORTED BY RDF with the specs in their current state. That 'metadata' use works ONLY when we know that the "identifying" graph IRIs denote their graphs, and WE HAVE EXPLICITLY SAID THAT RDF DOES NOT ASSUME THIS. A conforming RDF engine would be perfectly conforming if it refused to treat those subject IRIs as denoting the graph in these triples.  There is NOTHING in the RDF specs that say that a general IRI must be taken to denote what it conventionally identifies.  We do this only for datatype IRIs, and even getting that much into the specs was an uphill struggle; and in the case of graph labels in a dataset, we explicitly warn people to not expect this to be true (because it often isn't.) I know the Primer has to be simple, but please let us not put actual lies into it.
>> 
> 
> "RDF does not assume this" doesn't mean that RDF explicitly forbids it,
> no?

It does not forbid it, no, because it does not really forbid just about anything :-)  But there are two issues here that often get mixed up. It is one thing to say that RDF does not forbid writing such triples - of course, it allows that - but something else again to say that RDF allows you assume that when you do write them, they must mean what you intend them to mean. It is the intended meaning - in particular, the presumption that when the graph names are used in RDF triples, they will be understood as referring to the graphs - that is prohibited by the current RDF specs. We have said explicitly that no such presumption is warranted. So while of course anyone can write that 'metadata' RDF, also anyone else can, while reading it, treat the IRIs in it is denoting something other than the graphs, and the first author has no RDF-sanctioned grounds to object to this mis-interpretation. According to the RDF specs, using an IRI as a graph label in a dataset says **absolutely nothing** about what the IRI denotes, ie what the IRI is understood to mean when it is used in inside an RDF triple. The same IRI that labels a graph might denote a person or a time-interval or indeed just about anything, and still be used to label a graph. 

> I thought that we deliberately left that open for people to use
> graph IRIs as they see fit.

The question is, how can OTHERS know what they are seeing the IRIs as fit for? And the point is that the "obvious" interpretation of using an IRI as a graph label in a datset is not a valid RDF inference. So someone else cannot rely on it as a way to know that the IRI is supposed to be the name of the graph, even when the intended metadata is in the same dataset. 

> If it's an 'actual lie' (which I really
> don't think it is), then it's a bit of an issue, as a lot of people use
> graphs to do exactly that.

If they do so, then their data is at risk, because others use them in other ways, so interoperability is being compromised. Maybe we should say that they SHOULD NOT do this while publishing RDF data on the open Web. But in any case, we should not, in a Primer, give the impression that this "obvious" use is sanctioned or supported by the RDF specs, because it is not. As you say, it is not exactly prohibited, but it is what one might call emasculated. (Pardon the sexist presumption there.) 

Pat

> 
> Best,
> Yves
> 
> 
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Received on Monday, 25 November 2013 16:35:42 UTC