Re: shapes-ISSUE-30 (shape-and-data-graphs): Are shapes and data in the same graph? [SHACL Spec]

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On 04/12/2015 05:01 PM, Holger Knublauch wrote:
> One of the main selling points of RDF technology has always been the fact
> that instance and schema are represented uniformly. RDF Schema and OWL
> class definitions are instances (of metaclasses) themselves. This means
> that such data can not only be stored and shared together, but also be
> queried uniformly. In general, SPARQL queries can freely walk between
> meta-levels.
> 
> Many other formalisms such as XML and SQL databases have a stricter
> separation between those levels. If we agree on a similarly strict
> separation by making it impossible to query the shapes graph from the
> instances graph (and vice versa), then we may throw away a unique
> advantage that RDF technology has. I am generally not in favor of
> selecting the lowest common denominator for all use cases, only because
> certain cases may not have the best performance.
> 
> I understand that we need to maintain good performance, including the
> ability to use native query optimizations on database level where
> possible. Also there are cases where the shapes model is really totally
> separate from the database. Yet I believe there are also cases where
> being able to access the shapes definitions at runtime is beneficial.
> 
> In this discussion here, I believe we should distinguish between what we
> use in the SPARQL queries of the specification versus what optimized 
> implementations may do. I believe it should be doable to assume that - in
> the context of the spec - the shapes graph can be in the same dataset as
> the actual data. So by default we would have a single dataset and
> validation gets two parameters:
> 
> - the URI of the "instances" data graph (default graph) - the URI of the
> shapes graph

I would put this exactly the other way around, namely

  I believe that it should be doable to assume that - in the context of the
  spec - the shapes graph can be completely separate from the actual data. So
  validation has two parameters:
 - the "instances" data graph
 - the shapes graph

I believe that this setup is much cleaner than a design that *needs* to do
something special when the shapes graph is inaccessible from the data graph.
In this setup special things *can* but do *not* need to be done when the
shapes graph is accessible from the data graph.

[...]

> Regards, Holger

peter

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Received on Monday, 13 April 2015 14:35:27 UTC