Typed RDF - Was: Blank nodes must DIE! [ was Re: Blank nodes semantics - existential variables?]

> On 16 Jul 2020, at 16:18, David Booth <david@dbooth.org> wrote:
> 
> On 7/16/20 9:58 AM, Dan Brickley wrote:
>> I believe the big appeal of putting it all into the zone we call "literals" is that you get a kind of atomicity; that chunk of data is either there, or not there; it is asserted, or not asserted. With a triples-based (description of a ) data structure you have to be constantly on your guard that every subset of the full graph pattern is at least sensible and harmless, even when subsetting these chunks is often confusing or misleading for data consumers. I can't help wondering whether notions of graph shapes [ . . . ] could be exploited to create an RDF-based data format which had atomicity at the level of entire shapes.
> 
> +1
> 
> IMO the ability to manipulate chunks of data atomically -- arrays, n-ary tuples and hierarchical objects -- is a key requirement in developing a higher-level form of RDF.   This will include the need to conveniently construct and deconstruct such chunks in rules or query languages.
> 
> David Booth

I think we are getting somewhere close to the idea of typed RDF. 
I don’t yet have opinions on that yet, but have come across it 
reading a paper by Even Patterson ”Knowledge Representation in 
Bicategories of Relations" that extends the ideas
developed in Functorial Databases developed at MIT by David Spivak
to the category Rel of Sets and Relations (which intuitively fits RDF better,
though there is a translation between the two). It turns out that 
the Grothendieck Construction of a functor from a small bicateogry of
Relations to Rel, gives a typed RDF.

See: 
https://gitlab.com/web-cats/CG/-/issues/9

Is RDF typed? Well it may be that it is partly, or that it could
be moved in that direction. OWL partly goes in that direction with
ObjectProperties and DataProperties. If one thinks of objects as forming 
one big type not containing literals, and each literal type forming its 
own space, then one has have a light weight type system in RDF. 
This may have reasoning advantages. (mathematicians would need to be 
consulted). For example it looks like OWL allows one to specify a 
subtype of xsd:int that does not contain a certain range of numbers. 
Does it really make sense to think of things that could
satisfy those as containing elephants too? Would it not make more sense
to understand those as still covering integers? I think so. And it
is quite easy to see that this would make reasoning easier, as the
space to search would be smaller).

It is also interesting to note on this topic that Functorial databases
that have a beautiful simiplicity, had to be enhanced around 2013 by
adding a construction to fix types. Without that the morphisms between
database instances (functors) would allow names of people to also be 
exchanged when the structures were isomorphic. Essentially all elements 
of the database including literals were represented as blank nodes. 
This points to the distinction between literals and objects as 
being fundamental to all databases.

I am not sure if Evans has integrated the work on functorial databases
that keeps literals constant to his bicategories of relations. It would
probably be easy to translate the findings  as there is an isomorphism 
I understand between the two structures.

Henry Story

https://co-operating.systems
WhatsApp, Signal, Tel: +33 6 38 32 69 84‬ 
Twitter: @bblfish

Received on Thursday, 16 July 2020 14:59:33 UTC