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Turtle unlabelled blank nodes

From: Peter Ansell <ansell.peter@gmail.com>
Date: Mon, 22 Oct 2012 13:15:37 +1000
Message-ID: <CAGYFOCTGSss4cUrL6682soswMk53UpX+6=PSSMMLS=ZWGigQew@mail.gmail.com>
To: public-rdf-comments@w3.org

The Turtle W3C Working Draft (10 July 2012) supports unlabelled blank nodes [1]

The grammar for the Turtle format in this working draft contains the
following rule [1]:

    [6] 	triples 	::= 	subject predicateObjectList |
blankNodePropertyList predicateObjectList?

This rule seems to imply that a blank node property list, which is one
way that unlabelled blank nodes are referenced in the grammar, can
exist on their own without a following predicateObjectList.

However, the examples in the working draft only show the cases where
blankNodePropertyList is followed by a predicateObjectList.

Are the statements in the following turtle document valid according to
the 10 July 2012 draft?

    # Test non empty [] operator with no predicate or object following
the blank node
    @prefix : <http://example.org/base#> .
    [ :P "007"^^<http://www.w3.org/2001/XMLSchema#string> ].
    [ :P 8.1 ].
    [ :P "not a number" ].
    [ :P :Q ].
    [ :P <http://example.org/base#T> ].
    [ <http://example.org/base#P> 7 ].
    [ <http://example.org/base#P> "7" ].
    [ <http://example.org/base#P> "language literal"@fr ].

The reason that I am investigating this is that the OWLAPI Turtle
writer, which is used by Protege, among other applications, uses this
feature heavily to represent some types of OWL axioms. I found the
incompatibility when these documents failed to load using the Sesame
Rio Turtle parser.

The Turtle test suite in Sesame currently states that it contains
tests from [3], which seems to have been replaced by the Raptor test
suite located currently at Github. The test suite in the Raptor Github
repository had a test for these structures added recently as a failing
test with the comment "Add (currently) bad turtle forms of bnode
subjects" [4]. This is confusing, as it is not clear when they will be
valid, and if so, why they are failing tests currently. Any
clarification would be appreciated.


Peter Ansell

[1] http://www.w3.org/TR/2012/WD-turtle-20120710/#unlabeled-bnodes
[2] http://www.w3.org/TR/2012/WD-turtle-20120710/#grammar-production-triples
[3] http://cvs.ilrt.org/cvsweb/redland/raptor/tests/turtle/
[4] https://github.com/dajobe/raptor/commit/60f9398b4380c4e93cd70dda87fa57602b87a8f0
Received on Monday, 22 October 2012 03:16:06 UTC

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