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Re: Proposal to resolve ISSUE-102 (well-formed lists)

From: Dan Brickley <danbri@danbri.org>
Date: Fri, 9 Nov 2012 09:23:21 +0000
Message-ID: <CAFfrAFoN00Jp48NRiiKQmjqWF25daB=bQ7Ni-py7P2OwOwW1Cg@mail.gmail.com>
To: Richard Cyganiak <richard@cyganiak.de>
Cc: RDF Working Group WG <public-rdf-wg@w3.org>
On 9 November 2012 08:48, Richard Cyganiak <richard@cyganiak.de> wrote:
> ISSUE-102: Shall we highlight Turtle's list structures as "Well-Formed Lists" in one of our Recs?
> http://www.w3.org/2011/rdf-wg/track/issues/102
>
>
> PROPOSAL: Define the concept “well-formed list” in detail in RDF Schema, including a nice diagram. State that any use of terms from the collections vocabulary SHOULD be part of a well-formed list. Update Semantics to remove discussion of collections in 3.3.3. Update Turtle and RDF/XML to refer to well-formed lists when introducing the respective syntax shorthands. Send an email to OWL WG comments list informing them of this and suggest that future versions of OWL do the same.

re http://www.w3.org/TR/rdf-schema/#ch_collectionvocab

Use of the word 'SHOULD' somewhat frightens me, as it moves RDFS into
a very different role. Historically, we have limited ourselves to a
kind of passive, declarative specification, defining the meaning of
terms.

When SHOULD enters, we need to be very clear who we are shouting at,
and why. Is it an error to take a set of triples (a graph) and produce
a subset? Many of us do that all the time, using a variety of tools
(including APIs, grep, ...). Is it an error to share the results?
Privately? In small groups? Whose error is it if someone SPARQLs with
'?x rdf:first ?y' and pulls out just pieces of a list through a query
API? Or does something with sameAs to fold the list back on itself? If
our notion of error is grounded in patterns of truth, I think we have
the machinery. But this notion of 'SHOULD' seems more in a software
engineering mode.

What underlying concepts are needed for us to "State that any use of
terms from the collections vocabulary SHOULD be part of a well-formed
list" ? Does this rely on the notion of a "graph" in some sense? As we
saying that no graphs ought to exist whose use of
List/first/rest/next/nil violates some set of constraints. Is there
candidate text around somewhere for 'well-formed list'? I don't think
a picture will capture the subtleties. Must the elements of the list
be described with only bNodes? Can they have for example functional
properties that imply identity between list elements? (under which OWL
semantics).

A more declarative flavour of this would be to say there are two kinds
of RDF graph. Those that use rdf:List in certain troublesome patterns,
and those that don't. But how do those details look? What would an
rdf:GraphThatHasDodgyLookingLists definition look like? Can it be
expressed in SPARQL 1.1, partially or in entirety?

Dan
Received on Friday, 9 November 2012 09:23:48 GMT

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