W3C home > Mailing lists > Public > public-rdf-wg@w3.org > April 2012

Re: a new spin on contexts -- do they really help with vocabulary mapping?

From: David Wood <david@3roundstones.com>
Date: Wed, 25 Apr 2012 08:15:36 -0400
Cc: Pat Hayes <phayes@ihmc.us>, W3C RDF WG <public-rdf-wg@w3.org>
Message-Id: <862EC1D2-4E6B-4A7D-82AF-F94FA6D18552@3roundstones.com>
To: Sandro Hawke <sandro@w3.org>
That's a very useful analysis, Sandro.  Thanks.

> Alice is an organic chemist

This message is destined to go down in RDF history.  However, I'm left with the question, "who is Trudy in this scenario?"


On Apr 24, 2012, at 22:27, Sandro Hawke wrote:

> [This is a brainstorming discussion, maybe off-topic for the WG.]
> On Mon, 2012-04-23 at 00:45 -0700, Pat Hayes wrote:
>> First, regrets for next Wednesday, I will be driving through Texas. 
> I drove across the panhandle once.  Surely, you can just lash the wheel,
> put a rock on the gas pedal, and stretch out in the back seat to talk to
> us.....     (not that we'll be talking about this, from what I gather.)
>> Second, I have written up essentially the same proposal in a slightly different terminology which might (?) be more palatable, anyway it is there for inspection at http://www.w3.org/2011/rdf-wg/wiki/AnotherSpin
> I'm just going to respond, right now, to the middle of Why Bother,
> because I think everything flows from there.
> As background, I subscribe to the philosophy that the meaning of an RDF
> graph depends on the meanings of the predicates it uses.  So, to extend
> the semantics of RDF to include equality, you just *use* owl:sameAs.  To
> extend the semantics of RDF to include subproperty reasoning, you just
> *use* the predicate rdfs:subClassOf.   This seems very simple and
> elegant, although I will grant it has not been well understood or well
> deployed, to date, and isn't exactly how the specs are written.
> I don't see a need for rdf:inherits -- I think the semantics should,
> essentially, automatically 'inherit' each predicate.   I think this
> should be implemented, in the general (low performance) case, by having
> clients download inference rules from the predicate URLs. [1]
> Reasoners can be specialized to use a tableau algorithm, for example,
> instead of running rules, if the result will be the same (or predictably
> and usefully different, I guess).   
> Trying to understand the Why Bother section...   I like the chemistry
> example.   As I understand the science: there was Carbon, pretty well
> understood, and then suddenly a hundred years ago, it started to look
> like there was actually Carbon 12, Carbon 13, Carbon 14, and more.
> Unseen, unknown, until radioactivity was understood.  
> So, in RDF, we can imagine there's lots of data about chem:Carbon, and
> then suddenly, starting around 1912, we have iso:Carbon12, iso:Carbon13,
> etc.  Statistically, 99% of chem:Carbon is iso:Carbon12.  Only
> 0.0000000001% [2] of the chem:Carbon is iso:Carbon14, but still that
> little bit is enormously useful, eg for carbon dating.  Chemical
> formulas don't care about isotopes: propane is C3H8, whichever carbon
> isotopes are used in it.  When we're just doing normal chemistry, we
> want to ignore isotopes; when we're doing carbon dating, or looking at
> precise atomic weights, we do not.
> So, how do we do this in RDF?   Can we do it without contexts?
> Alice is an organic chemist, and all her software uses the chem:
> vocabulary.  Her experimental results all talk about chem:Carbon.  She
> doesn't care about isotopes.
> Bob is a radiochemist.  Pretty much all of his software uses the iso:
> vocabulary, because he works with specific isotopes.   His data includes
> lots of references to iso:Carbon12, and other isotopes.
> Things get interesting when Bob wants to use some of Alice's data, or
> Alice wants to use some of Bob's data.
> First attempt: use an OWL reasoner on the data, and mix in the "facts"
> that:
>        chem:Carbon owl:sameAs iso:Carbon12, iso:Carbon13, iso:Carbon14.
> This will probably work for some things, and completely break for
> others.  The chemical properties are the same, so that sounds okay.
> Nearly everything Alice findsa to be true for chem:Carbon is almost
> certainly also true for each of the carbon isotopes. 
> However, there are some properties (atomic weights, number of neutrons,
> rate of radioactive decay) which are different.   If some of that is
> given in the iso ontology, the reasoner will quickly determine (if it
> looks) that the combined ontology is inconsistent.
> We'd like something a little more like a subclass relation.  If these
> ontologies treated substances as classes containing, as instances, items
> composed of that substance, the mixin 'facts' could be:
>   iso:Carbon12 rdfs:subClassOf chem:Carbon
> That's much closer to true.  It could even be true, if chem:Carbon were
> designed with an understanding of isotopes, but in our scenario, it
> wasn't.   With the new understanding of carbon, the atomic weight is
> defined as that of carbon-12, but before they understood about isotopes,
> the atomic weight ended up being the combined atomic weights of the
> isotopes found in the carbon the chemists worked with.    So our naive
> chem:Carbon definition gives it a single atomic weight, which is not the
> same as any of the isotopes.    so that subclass rule isn't quite right
> either.
> Maybe that was Alice's experiment, measuring the atomic weight of
> Carbon.  She doesn't know about isotopes, so her answer wont be exactly
> the weight of any of the isotopes; it'll be the weight of whatever
> combination she happened to use.
> We have a world here where the ontologies line up 99% and maybe with
> some work we can get another .9% or maybe .99%.  But never 100%.
> There's carbon-12 and there's "carbon", which is a mixture of the
> various carbon isotopes as they happened to occur for that particular
> observer.
> Can contexts help with this?  Is it better to use the same term for
> these two concepts?   I wouldn't think so.
> I think the answer here is to use "shims", such as these "facts" I've
> used above.  I think people should publish various shims, for various
> purposes.   The shims are web documents which say how to map from data
> in one vocabulary to data with a similar meaning in another vocabulary.
> I'm not sure how much they should be OWL vs RIF vs Javascript (using
> some convention not-yet-determined).    I think the shims will have to
> be labeled in ways that help people, and sometimes machines, figure out
> which ones are best for their purposes and understand in what ways they
> are wrong/broken.  Maybe Bob writes one that allows him to use Alice's
> data, then publishes it for others to use under similar circumstances.
> I can see how to do that as long as we use different IRIs for the
> different notions of carbon.   If we used the same IRI but labeled the
> graphs in some way, I think it would get harder.
> (Change-over-time is a different use case, which I'd like to talk about
> separately.)
>    -- Sandro
> [1] Pat, I think you were in the room when I gave this talk.  I don't
> remember your reaction. 
> http://www.w3.org/2009/Talks/1026-semrus/#%2831%29
> [2] I love wikipedia.
Received on Wednesday, 25 April 2012 12:16:09 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 22:02:04 UTC