Re: RDF* and conjectures

good afternoon;

> On 2021-09-18, at 14:27:17, thomas lörtsch <tl@rat.io> wrote:
> 
> 
> ...
> 
> Please help me to understand:
> IIUC 
> SPARQL ASK queries return TRUE if the BGP that is asked for is either included or entailed locally to a graph (not across graphs) in the named graphs the query refers to in its request. 
> 
> So what you, James, are saying is that it is up to the user to decide which graphs to ask - which is a very important aspect w.r.t. Fabios general aim to control the scope of what is considered true, conjected etc. Do I understand that right?

[this is not _my_ claim.]
_for sparql_, section 13, describes constructing and querying the dataset (https://www.w3.org/TR/2013/REC-sparql11-query-20130321/#rdfDataset).

> If I do, then I’d like to add that the Named Graphs paper from 2005 by Carroll et al proposed some vocabulary that allows to express which graphs are to be considered 'accepted', merely quoted etc. I agree that something like that could go a long way towards standard - and flexible - graph semantics if it was properly declared and followed. Fabios proposal on first sight seems even more powerful - a very interesting perspective!
> 
> 
> Also the following is not quite clear to me:
> IIUC

[again, it does not matter, whether you understand _me_. the documents are what they are.]

> the Note on Dataset Semantics discusses named graphs semantics along the following 4 dimensions and no others:
> 1: if the name refers to the graph itself or something else (which is in an unspecified relation to the graph)
> 2: how named graphs in a dataset influence the truth value of each other
> 3: if named graphs are referentially opaque or transparent
> 4: if named graphs are types or occurrences
> 
> If this list is correct and complete then I understand that SPARQL ASK answers these questions as follows:

the ASK operator does not itself answer the questions.
section 13, which describes how to construct the dataset and how graph matching contributes to the interpretation of any expression,  does.

> 1: it does not answer this question, leaving the denotation of a graph name undefined

the sentence in 13.2.2 

    The IRI identifies a resource, and the resource is represented by a graph (or, more precisely: by a document that serializes a graph

can be read in a way which provides one answer to this question

> 2: it does answer this one, treating graphs as independent contexts

they are distinctly designated sets of statement to be combined into the dataset as per the prolog and made the target of graph patterns dependent on context.

> 3: it does answer this one, treating graphs as referentially transparent

this is not definitively answered as the combination method is suggested, but not stipulated.

> 4: it does answer this one, treating graphs as occurrences
>   (here I’m not entirely sure but as SPARQL does access graphs by name, not by their content…)

this is also not definitively answered, as it is described that repeated designators may or may not designate the same set of statements.

that there are variants is not material to the principal issue, as is it is not one of interoperability but of ability.
any given sparql implementation must have a complete answer to those questions or its operators will not close.

> 
> So when ASKing, SPARQL defines most aspects of the semantics of named graphs but not what the graph name denotes.

how can a process which must be applied to a concrete collection statements which were designated by graph names do one without the other?

> Using the graph name in the FROM clause refers to the graph. Using it to annotate the graph however is shaky territory: nothing in SPARQL prevents me from naming my graph with triples from Paris with the URI <paris.com>. So I have no soundly defined way to annotate that graph, right?

which graph was that?
why does it matter that there is no universal relation between the designator for a graph and the set of statements which it contains?
for a given implementation, there must be a necessary relation, but it need not be universal.

> Or can we exclude this possibility because it violates basic principles of web architecture w.r.t. URI collisions?

there is nothing in the recommendation which stipulates that the content must be the resource which would be retrieved given via http (or whatever) protocol were the designator to be treated as a location.
there are implementations in which the graph designators bear no necessary relation to resources in the internet.
it is even permitted to designate a graph wth a blank node.
yes, rdf originated as a way to describe web resources.
it has advanced well beyond that.

best regards, from berlin,

Received on Saturday, 18 September 2021 13:17:40 UTC