W3C home > Mailing lists > Public > www-rdf-interest@w3.org > February 2001

Re: Mapping External Triples Structures Into Your Own Systems

From: Graham Klyne <GK@ninebynine.org>
Date: Fri, 23 Feb 2001 23:10:33 +0000
Message-Id: <>
To: "Sean B. Palmer" <sean@mysterylights.com>
Cc: <www-rdf-interest@w3.org>
What's the problem here?  Given incomplete knowledge, you cannot infer what 
you need to know.

But then you dig a bit further, discover more information, and then you can 
infer what you need.

Seems quite right and proper to me.


At 05:13 PM 2/23/01 +0000, Sean B. Palmer wrote:
>Stop me where I'm wrong...
>Let's say we have the following snippet of easily understandable N3:-
>      @prefix : <http://infomesh.net/2001/02/ns1/> .
>      @prefix myns: <http://webns.net/2001/02/ns2/> .
>      :x :property1 :y .
>      :x :property1 myns:z .
>Now... :x is linked somehow to :y with :property1. No need to think of
>examples, that's all we need to know. Let's also say that it is
>*essential* for the machine that uses this schema to know that :x can
>take on the property1 of *both* :y and myns:z. Otherwise it won't
>Now, what if I take out the second line, and move it elsewhere, but
>replace it with another bit of information.
>      @prefix : <http://infomesh.net/2001/02/ns1/ > .
>      @prefix myns: <http://webns.net/2001/02/ns2/> .
>      :x :property1 :y .
>      :x :property1 :q .
>      :q = myns:p .
>My system is now completely broken. It needs to know, for some reason,
>that ":x :property1 :y, myns:z .", and this cannot be worked out from
>the information above.
>However, what if the Schema at http://webns.net/2001/02/ns2/ contained
>the following:-
>      @prefix : <http://webns.net/2001/02/ns2/> .
>      :p = :z .
>In other words, it needs to know that ":x :p1 myns:z". At the moment
>it knows that ":x :p1 :q", and also that ":q = myns:p". If my system
>could just work out that "myns:p = myns:z", then the thing would work.
>How can it get this knowledge... well (take a deep breath), if my
>program dereferenced the URI for the second schema (shock horror), it
>finds that it understands what the URI *means* in this context (it
>explicitly trusts that server, because I programmed it to). It did
>need to understand the HTTP, and the N3 needed to derive that fact,
>but at least it now correctly finds out that ":x :property1 :y, myns:z
>.", and the dang thing works at last. All because it dereferenced a
>Kindest Regards,
>Sean B. Palmer
>@prefix : <http://webns.net/roughterms/> .
>[ :name "Sean B. Palmer" ] :hasHomepage <http://infomesh.net/sbp/> .

Graham Klyne
Received on Friday, 23 February 2001 18:14:05 UTC

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