Re: defining the semantics of lists

On Mon, 18 May 2020 at 23:33, Patrick J Hayes <phayes@ihmc.us> wrote:

> 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>?



is this somewhere that the graph shape languages (shacl, shex, ...) could
plug in?

Dan

>
> 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
>
>
>
>