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Re: RDF*/SPARQL* syntax

From: Olaf Hartig <olaf.hartig@liu.se>
Date: Thu, 8 Aug 2019 11:50:13 +0000
To: "public-rdf-star@w3.org" <public-rdf-star@w3.org>
CC: Richard Cyganiak <richard@cyganiak.de>
Message-ID: <1565265011.8060.265.camel@lille71.ida.liu.se>
Hi Richard,

That's an interesting issue that you raise!

Before I respond, let me emphasize that I am not religious about what
the Turtle*/SPARQL* serialization syntax looks like as long as it serves
the purpose.   ...and if it does not have the issue that you point out
for the current serialization syntax, then great.

Now, I understand that the alternative you outline was meant to make
your point. However, let's consider it as an alternative proposal.

Then, this proposal indeed seems to have some advantages over the
serialization syntax as it is now. On the other hand, the current
serialization syntax is visually less different from the abstract
syntax. I mean, your proposed serialization syntax does not look like
nested triples anymore. Perhaps that's not necessary?

Even if it is not, there are some features of (nested) RDF* triples that
I cannot immediately picture how they may be captured in the alternative
serialization syntax you outline:

1/ What about RDF* triples that consist of multiple levels of nesting?
For instance, consider the following RDF* triple:

( ((:a, :b, :c), :d, :e), :f, :g ) .

Using the Turtle* syntax as it is defined at the moment, this triple
would be serialized as follows:

<< <<:a :b :c>> :d :e >> :f :g .

How would you represent this triple in the alternative serialization
syntax that you have outlined?

2/ What about (nested) RDF* triples that have a triple in their object
position? For instance, consider the following RDF* triple:

( :a, :b, (:c, :d, :e) ) .

Using Turtle* as defined at the moment, this triple would be serialized
as follows:

:a :b <<:c :d :e>> .

How would you represent this triple in the alternative serialization
syntax that you have outlined?


Thanks,
Olaf


On Wed, 2019-08-07 at 16:55 +0100, Richard Cyganiak wrote:
> 
> > On 5 Aug 2019, at 15:16, Olaf Hartig <olaf.hartig@liu.se> wrote:
> > 
> > On Mon, 2019-07-08 at 11:09 +0100, Richard Cyganiak wrote:
> >> [...]
> >> 4. I have concerns about the RDF*/SPARQL* syntax that I'd like to
> >> discuss at some point.
> > 
> > What are these concerns?
> > 
> > Are these concerns related to the abstract syntax (nested triples and
> > nested triple patterns)
> 
> No, the abstract syntax as proposed seems quite sensible and parsimonious to me.
> 
> > or to the Turtle* serialization format?
> 
> The concerns are related to the Turtle* and SPARQL* serialisation syntaxes. My concern for SPARQL* is bigger than for Turtle* as queries are more often written by hand.
> 
> In these syntaxes, a triple :s :p :o annotated with property-value :annoP :annoV is:
> 
>     <<:s :p :o>> :annoP :annoV.
> 
> In Turtle, a common and important idiom is to use the common-subject abbreviation:
> 
>     :resource1 a :SomeType;
>         :p1 :o1;
>         :p2 :o2;
>         :p3 :o3;
>         .
> 
> Similarly in SPARQL:
> 
>     ?resource a :SomeType;
>         :p1 :o1;
>         :p2 ?value2;
>         :p3 ?value3
> 
> The design of the Turtle*/SPARQL* syntax is such that it cannot coexist with this important idiom. To add an RDF*/SPARQL* annotation to either of the snippets above, one has to rip the snippet apart, undoing the common-subject abbreviation. For example:
> 
>     ?resource a :SomeType;
>         :p1 :o1.
>     <<?resource :p2 ?value2>> :annoP ?annoV
>     ?resource :p3 ?value3
> 
> This involves a lot of unnecessary typing and syntactic repetition. The result suffers from poor readability and does not make the intent visually clear.
> 
> There are various alternative syntaxes that would not share these shortcomings. As a straw man:
> 
>     ?resource a :SomeType;
>         :p1 :o1;
>         :p2 ?value2 <<:annoP ?annoV>>;
>         :p3 ?value3
> 
> Sp what I would like to see is a different way of extending Turtle and SPARQL with nested triples and nested triple patterns that does play better with idiomatic Turtle and SPARQL.
> 
> Richard


Received on Thursday, 8 August 2019 11:50:42 UTC

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