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Re: motivation for bNodes/existentials in RDF; note for parsers

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Fri, 5 Apr 2002 12:42:12 -0600
Message-Id: <p05101504b8d399bfd683@[65.217.30.94]>
To: "Seth Russell" <seth@robustai.net>
Cc: <www-rdf-comments@w3.org>
>Pat Hayes,
>
>I would like an authoritative interpretation of what the MT is telling us
>about blank nodes.   In particular if an rdf process reads a bnode from
>source A, and copies that node to a source B, but adds a uriref to the node
>(making it not blank),  has the process changed the meaning of the node ?

Not clear what 'changing the meaning' means. Has the process ADDED 
meaning? Yes, in the precise sense that its 'conclusion' (output) is 
consistent with, but not entailed by, its input. So it has not 
changed the meaning in the sense that it has denied what was input to 
it, but it has indeed altered the meaning in some precise sense. It 
is like the difference between being told that someone has a ball and 
concluding that Joe has a ball.
>For example:
>
>Source A reads:
>_:a  rdf:type :ball
>_:a  :hasColor :blue.
>_:a  :hasShape :round.
>_:a  :ownedBy :Seth.
>
>Source B reads:
><uuid:1615>  rdf:type :ball.
><uuid:1615> :hasColor :blue.
><uuid:1615> :hasShape :round.
><uuid:1615> :ownedBy :Seth.
>
>Is this tantamount to the process A reading  "Seth owns some (maybe only
>one) round blue balls."  and copying to B "Seth owns a round blue ball."?

No, the best way to render that output would be "Seth owns a round 
blue ball called '<uuid:1615>' ". Now, as long as everyone knows that 
'<uuid:1615>"'isn't *really* a name, then this indeed hardly amounts 
to saying more than was input to it. But how does one know, in 
general, which urirefs are supposed to be real names and which are 
only these, er, 'blank' names that only give existential import? Once 
the name is created and set loose upon the world, as it were, it 
loses all trace of its origin, and is just another uriref. And 
urirefs are names, on the web, right? Globally unique and supposed to 
last for ever. So you just created, for all time, and for planet-wide 
use, a permanent Name for this thing that nobody has a name for. If 
anyone else ever uses that name for anything else, global confusion 
could follow, so that uuid has now been used up, for ever. It can 
never be used by anyone else anywhere on the Web, ever again. I would 
say to the process that did that, are you SURE you want to publish 
that name? I wouldn't do it, myself.

Pat
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Received on Friday, 5 April 2002 13:42:12 GMT

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