Re: Against the notion of reification well-formed graph (i.e., atomicity)

The proposal (which does not originally come from me} has several options for 
the treatment of ill-formed RDF graphs, as indicated in the following wording:

* Implementations may/mustnot reject non-well-formed RDF graphs.

I'm going to add "must" to this to round out the alternatives.

peter



On 1/23/24 07:30, Doerthe Arndt wrote:
> Dear Peter,
> 
> Just to be sure (I am still forming an opinion): your proposal would be to add a definition of "wellformedness" (name might change) for  RDF graphs which is simply a property they may or may not have. Then, you envision that there are some applications which expect wellformed graphs as input and complain/warn in case of malformed input?  Or should wellformedness be a global requirement for anyone sharing an RDF graph?
> 
> Kind regards,
> Dörthe
> 
>> Am 23.01.2024 um 13:17 schrieb Peter F. Patel-Schneider <pfpschneider@gmail.com>:
>>
>>
>>
>> On 1/23/24 07:08, Thomas Lörtsch wrote:
>>>> On 23. Jan 2024, at 12:50, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
>>>>
>>>> On 1/23/24 06:30, Thomas Lörtsch wrote:
>>>>>> On 23. Jan 2024, at 12:22, Peter F. Patel-Schneider <pfpschneider@gmail.com> wrote:
>>>>>>
>>>> [..]
>>>>>>
>>>>>> What the proposal does talk about is RDF reifications, nodes in an RDF graph that are subjects of rdf:subject, rdf:predicate, or rdf:object triples.  The well-formedness requirement states that an RDF graph is ill-formed if it has a node that is the subject of a triple with any of these predicates and is not the subject of exactly
>>>>> Shouldn’t this be changed to *at least*? See my prior mail in response to Dörthe.
>>>>>> one triple with each of these predicates.  No bijection between triples and anything is either mentioned or implied.  The notion of well-formedness is completely syntactic.
>>>>
>>>> [...]
>>>>
>>>> The proposal is *exactly*.  Changing to *at least* could make it harder to optimize RDF reifications in implementations.
>>>>
>>>> As far as I can tell, multiple subjects, predicates, or objects is more difficult to optimize than missing subjects, predicates, or objects, but I haven't implemented an RDF triple store that optimizes RDF reifications.
>>> But what does it *mean*? Optimizations should only be applied after we know that it means what we want it to mean.
>>> I just realized that saying *at least* makes an implicit assumption about different terms in object position refering to the same entity in the realm of interpretation, i.e. a kind of owl:sameAs-ness. That may be way beyond what we want fix, and insofar saying *exactly* might be the safer and more restrained definition.
>>> Still it introduces a hint of opacity that I’m not happy with.
>>> Thomas
>>>> peter
>>
>> Not so.  The proposal makes no changes to the semantics of RDF.   (So far. There might be a semantic extension that does but I don't think that any change to the semantics, even if there is a semantic extension, is necessary.)
>>
>> So the formal RDF meaning of an RDF graph like
>>
>> :a rdf:subject :b, :c .
>>
>> is unchanged.
>>
>> Of course, users can add whatever intended meaning they want.  As far as I know, there is nothing in any RDF document that argues against users creating their own semantic extensions based on what RDF graphs mean for them.  There is not even any prohibition against users creating their own completely different meaning for RDF graphs.
>>
>> peter
>>
>>
>

Received on Tuesday, 23 January 2024 12:48:49 UTC