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Re: Another try.

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 21 Feb 2012 16:18:40 -0600
Cc: Andy Seaborne <andy.seaborne@epimorphics.com>, public-rdf-wg@w3.org
Message-Id: <4668CA76-EAF1-42A2-AB97-1387723A005C@ihmc.us>
To: Eric Prud'hommeaux <eric@w3.org>

On Feb 21, 2012, at 9:17 AM, Eric Prud'hommeaux wrote:

> * Andy Seaborne <andy.seaborne@epimorphics.com> [2012-02-21 11:44+0000]
>> On 21/02/12 07:56, Pat Hayes wrote:
>>> For conservatives among us, the opposite re-interpretation is always
>>> available. Any quad-graph can be thought of as a SPARQL dataset, by
>>> 'slicing' the quads according to their last argument, and
>>> re-declaring this parameter to be a graph label. However, to retain
>>> the semantic flexibility (ie to have the triples in each graph able
>>> to be re-interpreted differently in each labeled graph), we would
>>> have to modify the RDF semantics to allow for this graph-local
>>> context being involved in the truth recursions. And as already noted,
>>> it is simpler, and much less of a change ot the basic RDF model,  to
>>> do this by thinking of this construction in the quad-graph way as
>>> being a set of property-with-three-argument quads rather than as a
>>> collection of labelled sets of two-argument triples. And as so many
>>> of the 'natural' uses of datasets seem to want to take advantage of
>>> the apparent contextual' possibility of the graph label, and this
>>> option is only available in a quad-store format in any case, it seems
>>> comparatively harmless to attach the needed semantics directly to
>>> this quad store format, rather than tinker with the semantics of
>>> triples or try to make sense of graph 'names' which do not denote
>>> graphs.
>> I was wondering about existing vocabularies.
>> If I understand the quad proposal, then all existing vocabularies
>> are technically undefined because they never define P(S,O,G), only
>> P(S,O).
> And, imagining nimble fingers extended these definitions to include
> P(S,O,G), could they construct a definition for P(S,O,_) where the
> predicate means the same thing *in* *every* *graph*? This is of
> manifest importance; why else would we even write the definition.
> Enabling this, however, flies again in the face of those who want to
> "contextualize" the interpretation of graphs. The ability to say
> foaf:mbox is "an Internet mailbox associated with exactly one owner"
> is fundamentally in tension with wanting to say that foaf:mbox is
> context-dependent, and only the former leads to global knowledge
> exchange.

True. But we can resolve this tension somewhat by allowing some people to be quite clear that they do not intend to be understood contextually (which they do by refusing to contextualize their assertions, by not putting + at the end of any triples; and if they own the vocabulary, by stating as a semantic condition that their property extensions do no contain any quads, so that any use with a context is, in their opinion, false or contradictory) while still allowing others to treat their assertions contextually, or at any rate to import them and store them in a contextually nuanced datastore which is quite explicit about how *it* uses contexts. One man's plausible interpretation is another man's logical error, but at least we can provide some syntax to allow them to disagree about this explicitly. 

> If I understand the goal of the contextualist argument, is that the
> context influences our belief in assertions.

Well, actually, the above notwithstanding, the most compelling uses for 'contexts' are much more down-to-earth than this, and include the kind of keeping-track-of-date/time examples that Dan Brinkley was pointing out. And it is these mundane uses that I think will be seized upon most quickly and which the quads idea is best suited to handling. Time-sensitive data, that kind of thing. 

> Named graphs are a way of
> coursely controlling the assertions we let into our universe, and even
> predicating confidence in them. E.g. I'm trying to send PatH some mail
> and I'll presume the accuracy of the foaf:mbox in a FOAF file that I
> believe he controls and maintains. It turns out PatH uses mboxMD5sum
> instead (allergy to spam) so I look in the FOAF docs of people that I
> know because I don't trust other folks not to lie.
> In biology, as I expect in any detailed discipline, confidence is
> considerably more nuanced than that.

Right, which is why I wouldn't want to be understood as proposing a general mechanism for dealing with all these nuances. This is a research topic, whereas my proposal uses ideas from logic circa 1885.

> I could have a typical database:
> {
>    <http://w3.org/brief/MjU2> :mismatchesInCitation 0 .
> }
> <http://w3.org/brief/MjU2> {
>    human:OR4F5 :homologousTo mouse:Olfr1288 .
> }
> and ask for human genes which are exactly like mouse genes (0
> mismatches). This example is as simple as possible, but still has
> domain details. I suspect that 80% of our potential use cases are
> similarly detailed in some domain.
> Almost every question I ask in anger is one which is predicated on
> some context, but that doesn't mean that I want the interpretations of
> a predicate, e.g. :homologousTo, to vary with context. The semantics
> must enable predicated trust, but I suspect need not wrestle with the
> fact that there may be mutually incompatible assertions in the world.
> In my ignorance, I read PatH's proposal as trying to deal with
> potential incompatibilities by undermining the strength of their
> assertions rather than leaving that up to the consumer of the data.

No, I wasnt being anything like that ambitious. Just allowing one extra parameter for truth, to keep things easier. Its like having a stepstool to reach a higher shelf. Its not a general-purpose ladder, but it has a lot of everyday uses. 


>> The graph-local context view seems to preserve the vocabulary by
>> reinterpreting P(S,O).  It's less neat to have sets of triples +
>> graph labels, but it does seem to carry-over existing data.
>> Have I missed something?
>> 	Andy
> -- 
> -ericP

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Received on Tuesday, 21 February 2012 22:19:16 UTC

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