[ontolog-forum] NULLs and 3+1 vs. 4D ontologies (was Re: Knowledge graph

[Simon Spero <sesuncedu@xxxxxxxxx>]

On Tue, Jan 22, 2013 at 4:44 AM, Matthew West <dr.matthew.west@xxxxxxxxx> wrote:

That is precisely the problem with NULL. You don't know if it means not known, or does not exist. In principle it could mean either in any situation.

There is an analogous issue when relating 3+1D ontologies of Space+time to 4D ones when it comes to entities might  be considered to exist in time, but which may have no meaningful spacial extent.  

An good example of this are Fictional people (in worlds in which they are fictional, not in their fictional worlds).  These entities have a temporal extent, but assigning them to a spacial location is problematic. 

One could specify that they have a height, width, and length of 0, and unspecified x,y,z co-ordinates, but that does not distinguish them from a point whose location is happens to be unknown.  One could give them infinite spacial extent, so that they supervene upon the entire universe, but that is somewhat arbitrary,  requires that answers to questions about what exists in any given 3-space region as of the now  include Pegasus (and Fluttershy).  

One could stipulate that fictional characters supervene on physical things where information about them is held, but the act of  thinking about Fluttershy activates different neurons, and requires one to accept that you can move Fluttershy  with your mind. 

If one wants to say that x,y,and z extents/locations are meaningless for some types of abstract entities that can nevertheless have temporal extent, surely one needs to some sort of distinct value in ones coordinate space indicating that there is known to be no meaningful value (e.g. $\mathbb{R}_{\bot}$).  

This avoids confusion with  epistemic issues, but changes the commitments of ones ontology. 

Simon

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