Re: on values

If I undestand the issue correctly, the problem appears to be that :

(1) the SHACL specification needs to impose a *syntactic* constraint on the
third position in some kinds of RDF triples - specifically that the
syntactic form MUST NOT be that of an unreified blank node (i.e. "_:x")

but

(2) the specification refers to the *value* of this part of the triple,
where the syntactic form used to refer to the name is no longer relevant;
to be unoriginal,

    _:morningstar owl:sameAs :Venus.
    _:x sh:targetNode _:morningstar.

It may be possible to fix the document by explicitly  distinguishing
between the syntax and semantics; alternatively it may be less confusing to
define an abstract syntax for SHACL with a mapping from that syntax into
RDF.

Simon


On Dec 3, 2016 9:51 PM, "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
wrote:

Certainly it is fine for the SHACL document to state conditions about
SHACL-related things (SHACL graphs, SHACL shapes, SHACL constraints,
whatever).  But the current document goes much farther.

Of course, what the document currently says isn't anything that the document
should be saying and almost certainly isn't what is intended.  These parts
of
the document thus need to be fixed.

peter


On 12/03/2016 05:50 PM, Irene Polikoff wrote:
> Firstly, I do not know if it is OK or not for this value to be a blank
node. I’ll leave up to the editors to clarify.
>
> Secondly, assuming it is not OK, I believe it to be totally acceptable
for the SHACL spec to say that for SHACL shapes values of a specific
property must not be blank nodes. Users creating shapes should not be using
blank nodes as values for this property.  Such statement does not put any
requirements or restrictions or assumptions on all RDF graphs. It only
concerns itself with how shapes must be specified.
>
>> On Dec 3, 2016, at 7:57 PM, Peter F. Patel-Schneider <
pfpschneider@gmail.com> wrote:
>>
>> That is indeed what you said.  Prohibiting the value of sh:targetNode
from
>> being a blank node says something about all RDF graphs.
>>
>> This is what the wording in the SHACL document is stating.
>>
>> peter
>>
>>
>> On 12/03/2016 04:45 PM, Irene Polikoff wrote:
>>> This is not what I said
>>>
>>>> On Dec 3, 2016, at 5:46 PM, Peter F. Patel-Schneider <
pfpschneider@gmail.com> wrote:
>>>>
>>>> The SHACL spec can say something about all RDF graphs?  That doesn't
make sense.
>>>>
>>>> peter
>>>>
>>>>
>>>> On 12/03/2016 02:44 PM, Irene Polikoff wrote:
>>>>> By saying so in the spec.
>>>>>
>>>>>> On Dec 3, 2016, at 4:09 PM, Peter F. Patel-Schneider <
pfpschneider@gmail.com
>>>>>> <mailto:pfpschneider@gmail.com>> wrote:
>>>>>>
>>>>>> But how can the value of sh:targetNode be prohibited from being a
blank node?
>>>>>
>>>
>