Bound and Unbound Datasets

It looks to me like we have two very different camps concerning 
datasets.    ISSUE-131 has brought this to light again, but the camps 
long predate that issue.  The division is between the people who have 
been using datasets with application-dependent semantics for a long time 
and the people who want to build things which require standard 
interoperable semantics for datasets.    I'm in a latter camp, and was 
arguing for it for a long time, but I decided some months ago I could 
live without standard semantics via a very convoluted mechanism.  I 
agreed to document that mechanism, but as I have contemplated doing so, 
I've been dragging my feet because it's pretty weird and I think the 
group wont like it.    (Talking off-list to Pat about it yesterday, I 
think it's safe to say he hated it.)

So I have an alternative proposal.  Let's have two kinds of datasets:

  * "Unbound" datasets are what's been in SPARQL and rdf-concepts so 
far.   According to the standard they are just structure, with no 
semantics.  In practice, their semantics are determined by the 
application in which they are used.

  * "Bound" datasets have the following semantics:
       (1) for the dataset to be true, the default graph must be true;
       (2) graph names denote the graphs they are paired with.

I suggest we indicate a dataset is bound by putting the magic triple { 
<> a rdf:BoundDataset } in its default graph.   (This triple would be 
treated specially in the RDF semantics for any system which 
implements/recognizes bound datasets; to other systems (eg SPARQL) it's 
just another triple.)  If a dataset does not have this flag, it's 
unbound.   Of course, being unbound, it has application-specific 
semantics and so an application may choose to treat it as bound.

I think this would solve a lot of problems, and not raise too many.     
I expect many of the folks who wanted us to standardize named graphs, 
fix reification, etc, when this group was chartered, would much prefer 
having this option to having only the half-solution that's in our specs now.

       -- Sandro

Received on Monday, 3 June 2013 15:34:06 UTC