Re: thisiness

On 25 Mar 2011, at 13:36, Nathan wrote:

> Henry Story wrote:
>> On 25 Mar 2011, at 12:38, Gregg Reynolds wrote:
>>> (BTW, there are no unlabeled nodes; what seem to be unlabeled nodes are in fact anaphorically or indexically labeled.  An unlabeled circle in a diagram is still a symbol, a kind of indexical label; where nesting is used syntactically to indicate a blank node, the syntactic device of nesting can be taken as a kind of indexical label or symbol.  In other words, the difference is not between labeled and unlabeled, but between persistently and transiently labeled (or: between rigidly and contigently labeled) nodes.)
>> yes, that is what I was getting at in my last post. Blank nodes allow non rigid designation. URIs tend to be rigid designators. Somehow in philosophy this distinction seems to have been very helpful. It would be interesting to follow through on this parallel and see if we don't find the same usage and value on the semweb.
> We have the term "blank node identifiers" which leads many to believe that the identifier names the blank node, but there is no scope for that name, so they are non-rigid designators. The problem is that now often many see certain sets of triples as being associated with a name somehow  (as in sparql, the ?g, and linked data, the <uri> you GET) which gives a scope for the name, and thus the expectation is that blank node identifiers are rigid designators within the scope of that name. (As in, a name which acts as a namespace and defines a universe within which blank nodes can be both quantified and identified/named).
> Blank nodes are pretty much existentially bound variables with a quantifier whose scope is the entire graph, so when you have a name for two graphs and the name is the same, it follows that they are thought of as bound variables rather than free variables.
> Even if the above were made so in some way, we'd arguably end up with even more unexpected functionality when merging graphs associated with different names, and when no name is present.

And part of the reason people identify blank nodes with uris is that the use of the one versus the other has not been made clear. We should work out the pragmatic, philosophical and logical spaces where blank nodes give benefits. 

So if I describe someone using a blank node, then it is not possible to speak of the person using a URL in my namespace. This removes a certain identification responsibility from me. 

If I remember correctly - Harry Halpin might have this more freshly in his mind - Gareth Evens in "The Varieties of Reference" has a section on the importance of being able to distinguish objects if one wants to name them. He claimed - if I remember correctly - that it is not possible to name any of two identical balls rolling around in a basin, because if one were to be shown any of the balls one would have no way of assigning the name to one or the other of them. Here it seems one can tell that there are two balls in the basin, but not be able to give them names. If this reasoning is correct then there is a fundamental problem with arbitrary skolemisation of blank nodes. 


> Best,
> Nathan

Social Web Architect

Received on Friday, 25 March 2011 12:52:04 UTC