RE: Subjects as Literals


The fact that

    "basically, all the upper levels of the Semantic Web layer 
    cake are not based on RDF but on generalised RDF"

(see also my list of concrete citations at [1]) makes it, in my humble
opinion, essentially mandatory for an RDF working group to standardize
generalized RDF, i.e. subjects and bnodes in all positions of a triple.

In addition, I like your idea of having a "classic" syntactic fragment with
traditional RDF syntax, so older systems (or those for which their
implementers decide to not go to generalized RDF) will still have a standard
to conform to.


[1] <>

>-----Original Message-----
>From: []
>On Behalf Of Antoine Zimmermann
>Sent: Tuesday, July 06, 2010 9:54 PM
>To: Ivan Mikhailov
>Cc:; Semantic Web
>Subject: Re: Subjects as Literals
>Ivan, all,
>Le 06/07/2010 18:00, Ivan Mikhailov a écrit :
> > After 7 days of discussion, are there any volunteers to implement
> > proposal? Or you specify the wish and I should implement it (and
> > Kingsley should pay) for an unclear purpose? Sorry, no.
>Not only there are volunteers to implement tools which allow literals as
>subjects, but there are already implementations out there.
>As an example, take Ivan Herman's OWL 2 RL reasoner [1]. You can put
>triples with literals as subject, and it will reason with them.
>Here in DERI, we also have prototypes processing generalised triples.
>Other reasoners are dealing with literals as subjects. RIF
>implementations are also able to parse triples with literals as
>subjects, as it is required by the spec.
>In addition to the existing implementations, it should be noticed that
>the main standards built on top of RDF(S) (SPARQL, OWL 2, RIF) are all
>using generalised triples instead of the restrictive RDF triples. So,
>basically, all the upper levels of the Semantic Web layer cake are not
>based on RDF but on generalised RDF...
>Some people mentioned scalability issues when we allow literals as
>subject. It might be detrimental to the scalability of query engines
>over big triple stores, but allowing literals as subjects is perfectly
>scalable when it comes to inference materialisation (see recent work on
>computing the inference closure of 100 billion triples [2]).
>Considering this amount of usage and use cases, which is certainly meant
>to grow in the future, I believe that it is time to standardised
>generalised RDF. In addition, there are readily available serialisations
>for it (N3, or a straightforward extension of N-triple or Turtle) and a
>backward compatible extension of RDF/XML has been proposed in this
>thread (by Sandro Hawke).
>A possible compromise would be to define RDF 2 as /generalised RDF +
>named graphs + deprecate stuff/, and have a sublanguage (or profile)
>RDF# which forbids literals in subject and predicate positions, as well
>as bnodes in predicate position.
>Then SPARQL, OWL 2 and RIF would really refer to RDF 2 instead of each
>redifining generalised RDF. People implementing optimisations of triple
>stores would be implementing a W3C-approved part of RDF (namely, RDF#),
>just like people implementing OWL 2 QL implement part of OWL 2 for
>efficient data indexing and query answering.
>Honestly, it's just about putting a W3C stamp on things that some people
>are already using and doing. Just like named graphs and other stuff.
>Plus, it's an easy one since the semantics is already there.

>[2] Jacopo Urbani, Spyros Kotoulas, Jason Maassen, Frank van Harmelen,
>and Henri Bal. "OWL reasoning with WebPIE: calculating the closure of
>100 billion triples" in the proceedings of ESWC 2010.
>Antoine Zimmermann
>Post-doctoral researcher at:
>Digital Enterprise Research Institute
>National University of Ireland, Galway
>IDA Business Park
>Lower Dangan
>Galway, Ireland

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Received on Tuesday, 6 July 2010 20:56:08 UTC