Re: How would option b) on the last straw poll of 12 March work?

* Peter F. Patel-Schneider <pfpschneider@gmail.com> [2015-03-15 12:55-0700]
> A few questions and comments.
> 
> 
> Is this the entirety of SHACL or just the core language?  The language here
> does not cover closed shapes, exclusive or, global constraints, maximum
> cardinality of 0, non-datatype type matching, or datatype facets.

Agreed, it seemed wisest to start with a conservative subset and add.
What is "non-datatype type matching"?


> What happens with cardinalities that are not integers, e.g.,
> "3.1"^^xsd:double.

Is it worth enumerating the behavior in case of schema violations?
Does OWL say what happens with <X> :allValuesFrom "abcd"?


> Several of the RDF examples don't match the abstract syntax, e.g.,
> my:UserShape.

Can you point me a little closer at the mismatch?


> What happens if a node encodes both a property constraint and an and
> constraint, or any of the the other combinations?  What happens with
> structure sharing, e.g., a sh:property and sh:inverseProperty link to the
> same node?

I think half of the answer is in the RDF parsing rules. How does OWLs
Mapping to RDF graphs handle this? I wouldn't expect disjoint axioms
to prevent this in e.g. RL. That said, we could have OWL schema that
enumerations disjunctions and if people author schemas with violate
them, that's their problem.


> What is the basic operation in SHACL?  Does it take one RDF graph, one RDF
> dataset, or multiple RDF graphs and datasets?

So far, 6. Matching only defines matching for a `focus node` in an RDF
graph. I expect we'll want more expressivity in the core language once
we gather use cases from e.g. Jeremy Carroll.


> What is evaluation of a term?  What happens if there are multiple values?

fixed "property constraint matches" to read
[[
The "matching triples" is the set of triples in the graph with the
subject node of the `focus node` and a predicate of the `property
constraint's` predicate.  Evaluation of a property constraint produces
true if each of the following is true:

  If the property constraint has a `minimum cardinality` greather than 0,
  the `matching triples` number at least that minimum cardinality.

  If the property constraint has a `maximum cardinality` greather than 0,
  the `matching triples` number no more than that maximum cardinality.

  If there is a `term constraint` present, for each object in
  `matching triples`, that object matches (see 6.2…).
]]

That last condition could also reference a "term constraint matches"
analogous to "triple constraint matches" to serve as the prototype for
`note type matches`, `datatype matches`, `value set matches`, `value
shape matches`. Your advice?


> The specification appears to be ill-founded on recursive shapes over data
> loops.  I can't tell for sure because there is no formal basis.

We can add a set visited:([node,shape]) to the shape matches function
to provide an opperational strategy for eliminating infinite
recursion. Is that useful in the this semantics?


> peter
> 
> 
> On 03/14/2015 05:34 PM, Eric Prud'hommeaux wrote:
> > * Peter F. Patel-Schneider <pfpschneider@gmail.com> [2015-03-12
> > 13:56-0700]
> >> There were a number of WG members who voted for: b) The main
> >> specification shall include the higher-level language constructs only
> >> and the rest shall be defined in add-ons.
> >> 
> >> Can any one describe how this option would work?  Would there be a
> >> single way of defining the meaning of the entire language (main spec
> >> and add-ons) or would there be several ways of the defining what
> >> constructs mean?
> > 
> > As a down-payment, I offer
> > <http://w3c.github.io/data-shapes/semantics/>. I hope to produce a start
> > on an axiomatic semantics and a SPARQL semantics tomorrow.
> > 
> > 
> >> peter
> >> 
> > 

-- 
-ericP

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Received on Monday, 16 March 2015 00:40:02 UTC