Re: blank nodes (once again)

>>>>> Reto Bachmann-Gmuer <reto.bachmann@trialox.org> writes:
>>>>> On Mon, Mar 14, 2011 at 5:56 PM, Ivan Shmakov wrote:

[…]

 >> But my question is itself tangential to the equivalence of these
 >> graphs.  Instead, I wonder, if I've assimilated this above
 >> representation into an RDF store, and going to assimilate its exact
 >> twin again, does this later assimilation change the /knowledge/
 >> contained within such a store, or not?

 > No. The /knowledge/ will remain the same,

 Indeed, both before and after reading the second serialization,
 I'll only know that at least one source asserts that Joe has at
 least one dog.

 > even though the store might no longer by lean after adding the two
 > identical graphs.

 ACK.  Thanks!

 However, I feel somewhat uneasy about having a store changed
 while the knowledge contained within it remains exactly the
 same.  Is there a way to avoid it?  Are there other known issues
 like that?

 Treating this particular issue doesn't seem overly difficult.
 First, we may split the source graph into subgraphs so that each
 of the subgraphs will contain only those blank nodes that are
 linked to each other only via arcs and other blank nodes, and
 only those non-blank nodes that are exactly one arc away from
 any of the blank nodes contained.  (A procedure similar to the
 one described in CBD.)

 Then, serializing the resulting subgraphs using a kind of
 “canonical” representation (which, in particular, imposes an
 ordered and stable blank nodes naming), and hashing them, the
 duplicate statements and whole subgraphs could be detected and
 removed from the store.

 >> I'm quite certain that after I've received the first bit I now have
 >> a bit more knowledge about the World.  However, I'm not so sure that
 >> the second bit gives me any more knowledge, since I still have no
 >> rational means to tell, whether the dog I'm told of this time is the
 >> same or different to the one about which I've already known.

 > You don't know anything more, except maybe that two sources assert
 > that Joe has a dog.

 If there were indeed two sources.

[…]

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