W3C home > Mailing lists > Public > www-rdf-logic@w3.org > June 2002

Re: the mythical RDF inference engine was: Re: What is truth anyways?

From: patrick hayes <phayes@ai.uwf.edu>
Date: Wed, 12 Jun 2002 15:16:50 -0500
Message-Id: <p05111a0fb92d57bea4c2@[]>
To: "Jonathan Borden" <jonathan@openhealth.org>
Cc: www-rdf-logic@w3.org

>patrick hayes wrote:
>>  >Gentlemen,
>>  >
>>  >I'm getting rather frustrated. Perhaps it is a mistake to write a model
>>  >theory for RDF, as it appears too constraining.
>>  What it constrains is what RDF inference engines are supposed to do.
>>  I WANT that to be constrained.
>I've never seen this so called 'constrained' RDF inference engine,

Neither have I, but it doesnt matter: I don't need to see a 
particular engine. What I meant was 'any engine that draws RDF-valid 
inferences'. I don't care HOW it does that. And to be fair, I would 
allow RDFS-valid.

>every _useful_ piece of software I've seen has extended this base RDF
>interpretation in some way from something like implementing
>daml:UniqueProperty to implementing a more extensive logic engine such as in

Look, I don't mean to suggest that this kind of thing shouldn't be 
done, or should be somehow outlawed. You are right that not much 
useful inferencing can be done in RDF; I think that is widely 
acknowledged. But I do think it will be a complete disaster - taking 
us back ten years, in effect - if such 'extended' inferences are all 
called 'RDF inference'. If it were all only for human consumption, of 
course, it wouldn't matter all that much what we call it: humans can 
read the published documentation and figure out what it going on. But 
software agents can't do that, and it is the software agents which 
are going to be inputting, reading, manipulating, drawing conclusions 
from and outputting (as future input to other software agents) all 
this RDF. If there's a CWM agent out there  disguised as an RDF 
agent, and my RDF agent reads its output, then all of *its* 
inferences are likely to be corrupted by invalid RDF conclusions that 
the CWM agent has drawn.  I just want each spec to wear its meaning 
on its sleeve, as it were, *as part of that spec*. And CWM and N3 are 
NOT parts of the RDF spec; and in fact, it is easy to prove that the 
claimed meanings for much of N3 are not writable in anything that 
could possibly conform to the RDF spec.

>Indeed since base RDF itself is just a bunch of assertions, I'm not sure
>what inferencing you can do _with RDF alone_ rather it seems just the
>mechanism for carrying 'facts'. I worry that all this emphasis on
>inferencine _within_ RDF is over constraining the ability to do inferencing
>_on_ RDF.

The problem is that last phrase is meaningless. Writing all the 
triples backwards is inferencing on RDF. Erasing the RDF and 
replacing it with a quote from the Koran is inferencing on RDF. If 
you disagree, tell us what YOU mean by inferencing on RDF.

>So why not just say that RDF is a bunch of assertions

Becasue that is an extremely dangerous thing to say: it sounds 
meaningful but in fact is meaningless. A bunch of assertions *in what 
language*?? In RDF? If so, then it is INCORRECT to use non-rdf-valid 
processes on them. Or are they, as Tim and Dan apparently want to 
say, a bunch of assertions in English? In which case of course you 
can infer whatever you are smart enough to figure out from them, but 
the poor software hasn't a hope in hell. Or are they maybe a bunch of 
assertions in (RDF+RDFS+DAML+OWL+....)? In which case, which 
inference rules should the software use (can it use the ones in 

>and forget about this
>pure RDF inferencing engine that doesn't seem to exist and let the folks who
>care about inferencing decide what inferences might be drawn from a certain
>bunch of facts and be done with it.

The whole point of having a precise account of meaning in the 
language spec is to sanction some inferences and not others. If we 
can allow anyone to draw any conclusions from an RDF graph, then RDF 
doesn't differ from XML. In fact, it doesn't differ from ASCII or 
graffiti: its just character strings that you can do whatever the 
hell you like with and call it inference. So why are we even 
bothering with it?


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Received on Wednesday, 12 June 2002 16:16:55 UTC

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