Re: PG mode and SA mode

Hi Pat,

Thanks for your valuable feedback. I understand the points that you
make and agree that they are important.

Olaf


On Wed, 2019-09-18 at 14:12 -0700, Patrick J Hayes wrote:
> > On Sep 18, 2019, at 11:53 AM, Olaf Hartig <olaf.hartig@liu.se>
> > wrote:
> > 
> > Dear all,
> > 
> > There has been some confusion about the modes I have mentioned in
> > some of the 
> > other threads (PG mode and SA mode).
> 
> …
> 
> BTW, I suggest that a good way to compare and contrast is to look at
> what is entailed by a graph, using test cases. 
> For example
> 
>  ( (s,p,o), p2, o2 )  
> ?entails?
>  (s,p,o)
> 
> PG yes, AS no.
> 
> > Therefore, I would like to get your opinions on the following
> > questions.
> > What do you think are the merits of the PG mode versus the SA mode,
> > and vice 
> > versa?
> 
> The SA mode seems far more rational than the PG mode, given that
> annotations may be used to qualify or even deny the inner triple. But
> I also think that this entire language of ‘modes’ is a really bad
> idea for a standard (see below.) 
> 
> > Do you have a clear preference for one mode over the other?
> 
> Yes. It is trivial to imitate PG mode in AS, by simply asserting the
> inner triple in the graph. It is impossible to imitate or embed AS
> mode in PG, which alone should rule it out. But there are other
> arguments. In AS (not PG), the content of the graph - what it says -
> is entirely contained in the triples of the graph; any other
> convention violates one of the design principles of the RDF model. In
> AS (not PG), all the conventional apparetus of RDF graph checks - the
> idea of lean graphs, checking for simple entailment and so on -
> remains unchanged, and the semantics of RDF graphs is unchanged. All
> of this weights very heavily on one side of the scale.
> True, there is a small cost for AS: some triples need to be written
> out twice in a surface syntax; but this seems like a fairly trivial
> cost, and in any case, extending a surface notation to allow links to
> other triples, using IDs or some other convnetion, could eliminate
> this, and might well be a useful line of investigation ion any case. 
> 
> > What do you think about introducing both modes in a specification
> > of the RDF*/
> > SPARQL* approach?
> 
> First, these are not two ‘modes’ but two languages, indistinguishable
> in syntax but with different semantics. That is a truly terrible
> idea. The only possible advantage would be to save some typing effort
> for those who wish to use the PG convention; but the potential for
> confusion is huge. Every app that uses RDF* will have to have checks
> and switches to decide which method to use to process a graph; graphs
> written one way will get processed using the other convention, with
> downstream consequences which will likely be untraceable to their
> source; and so on. 
> 
> (Sorry I have not been as active on this list so far as I had
> intended to be, but maybe this will make up for lost time.)
> 
> Pat Hayes
> 
> > 
> > Thanks,
> > Olaf
> > 
> 
>

Received on Friday, 20 September 2019 08:36:17 UTC