Re: defining the semantics of lists

Focussing on the key issue:

> On May 18, 2020, at 4:06 PM, thomas lörtsch <tl@rat.io> wrote:
> 
> 
>> On 18. May 2020, at 18:43, Patrick J Hayes <phayes@ihmc.us> wrote:
>>> On May 18, 2020, at 11:26 AM, Cory Casanave <cory-c@modeldriven.com> wrote:
> 
>>> We have an existing capability for managing sets of facts - the graph. The graph is already a "closed" set of facts. What we can't express is that a graph may be complete for a specific set of types or a specific set of predicates about a specific set of types. With that capability we could express a closed set - something that is REAL in our world. 
> 
> That sounds like a good approach.
> 
>> Yes, that ability – to say explicitly, in the data, that a certain set of data is complete wrt some kinds of information – would enable closed worlds to be reasoned about in an open-world reasoning framework. It is not easy to see how to do this, however. I have thought about this on and off for about a decade or more, and have not come up with a workable general way to do it. 
> 
> Would very fine grained Named Graphs (*) help? Rather Named Triples that can be grouped to Graphs in arbitrary ways (virtual/nested/overlapping/fluid Named Graphs if you want). May no scale super well but let’s not do early optimization. 

I do not follow what you mean here by ‘fine grained'. Named graphs would certainly help, indeed are arguably essential. 

>>> A "list" is then just an ordering of the things in a closed graph.
>> 
>> Nope, that does not work. Just listing the things is not enough, you also need a way to say what kinds of facts are being ‘closed’. For example, a list of employees might be complete in the sense that it lists them all, but not in the sense that it says everything that can be said about them. 
> 
> I’m quite puzzled by this objection. The relation is employeeOf, not everythingThatCanBeSaidAboutEmployeeOf.

Yes, but where is it specified that the graph is ‘closed’ (ie supports closed-world reasoning) for assertions involving employeeOf but not for, say, BrotherOf? That is the what is needed, a way to say ’the data in this graph is complete for assertions of <this kind>'. How do we specify <this kind>?

Pat

> What logic mechanism are you referring to here? If we are up against such greedyness then we are in a much worse situation than I thought.
> 
> 
> Thomas
> 
> 
> (*) with a little vocabulary addition that allows to refer to Named Graphs with sound, denotational semamtics

The semantics of named graphs has been developed quite throughly in https://www.researchgate.net/publication/234804495_Named_Graphs_Provenance_and_Trust

Received on Monday, 18 May 2020 22:30:00 UTC