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Re: Annotation syntax [was: SPARQL* test suite]

From: Holger Knublauch <holger@topquadrant.com>
Date: Thu, 3 Sep 2020 13:14:27 +1000
To: public-rdf-star@w3.org
Message-ID: <92d2d024-1180-2106-eecc-8b0e6b429592@topquadrant.com>

On 2/09/2020 23:17, Olaf Hartig wrote:
> On onsdag 2 september 2020 kl. 13:55:46 CEST Andy Seaborne wrote:
>> On 02/09/2020 09:04, Olaf Hartig wrote:
>>> Dear all,
>>> I am intrigued by the idea to add a second option to the Turtle* syntax
>>> such that PG mode and SA mode can be explicitly distinguished from one
>>> another. In fact, now I wonder whether such a distinction can even be
>>> built into the RDF* data model (it can, see below).
>>> The only issue with this new "PG mode option" for Turtle* is that it works
>>> only for annotations that have the annotated triple in the subject
>>> position.>
>>> Take, for instance, Holger's example:
>>>> ... instead of
>>>>        :bob :age 23 .
>>>>        <<:bob :age 23>> :certainty 0.9 .
>>>> we can simply (alternatively) write
>>>>       :bob :age 23 {| :certainty 0.9 |} .
>>> That works. However, the following Turtle* expression (assuming SA mode)
>>> cannot be written by using the proposed alternative syntax option.
>>>        :bob :age 23 .
>>>        :alice :disbelieves <<:bob :age 23>> .
>>> Perhaps this limitation is not an issue. The notion of edge properties in
>>> Property Graphs has the same limitation after all. What do you think?
>> I see {|...|} as convenience syntax.
>> The same happens with bnodes in the object position - if a bnode is
>> object in two triples, you can't use [] notation, you have to use _:label.
> Makes sense.
>> On the syntax :
>> what about:
>> :bob :age 23 {| :origin
>>                      [ :source <http://bob.name/> ;
>>                        :retrieved "2020-09-02"^^xsd:date ]
>>                |} .
> Yeah, I think that we may add this option as well. Good idea.
>>> Ignoring this potential issue, I thought a bit about my question from
>>> above: Can such an explicit distinction between SA mode and PG mode be
>>> built into the RDF* data model itself?
>> I need to work though the details in your message but could I ask what I
>> do wonder what the value of having the distinction in the formal model,
>> compared with, say, a data design pattern "PG mode is SA where each
>> referenced <<>> triple is also in the data graph".
> The problem is that the assumption of which mode to use would not be explicit
> in this case. For instance, if I put a Turtle* file online, your client does
> not know whether I meant this to be considered in PG mode or in SA mode. By
> using << .. >> exclusively for SA mode and {| ... |} exclusively for PG mode,
> we can be explicit. My proposed formalism carries over this distinction to the
> abstract data model.

I very much support this idea of using the syntax to define a dialect. 
If I understand things correctly then PG mode is a subset of SA mode, 
i.e. the space of possible PG graphs is smaller than that of SA graphs. 
So I would assume that SA mode also still needs to allow << ... >>> 
syntax for the non-asserted triples. However, it seems that PG mode 
could be defined as the subset of SA that can be expressed through the 
{| notation, basically capturing what property graphs allow. This is 
probably another way of saying what Olaf has worked out with his more 
mathematical/formal spec?

BTW, the use of triples as objects could be expressed using an inverse 
path, e.g.

:bob :age 23 {| ^:disbelieves :alice |}

although if Property Graphs don't support that then maybe RDF*'s PG mode 
also shouldn't.


> Olaf
Received on Thursday, 3 September 2020 03:14:44 UTC

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