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Re: SPARQL paths and N3 paths: some quick thoughts.

From: Andy Seaborne <andy.seaborne@talis.com>
Date: Thu, 25 Feb 2010 11:00:45 +0000
Message-ID: <4B86585D.6070509@talis.com>
To: Dan Connolly <connolly@w3.org>
CC: public-rdf-dawg-comments@w3.org, public-cwm-talk@w3.org, Tim Berners-Lee <timbl@w3.org>

On 27/01/2010 6:59 PM, Dan Connolly wrote:
> I should have copied the comments list last Friday when I started this
> thread...
> http://lists.w3.org/Archives/Public/public-cwm-talk/2010JanMar/0002.html


Thank you for pointing out the thread on public-cwm-talk.

On the specific issue of character use, the property paths draft follows 
N3 in using ^ for backwards paths. It uses "/" for forward paths. The 
"!" character is used in filter functions in SPARQL as the "not" 
operator. That does not preclude the use of "!" in property paths 
although it does carry a very different meaning. On balance, the working 
group feels that "/" is more appropriate.

By the way, we have also received a comment [1] that makes a suggestion 
for describing sets of properties by exclusion.

In [2] there is discussion of including expressions in N3. Property 
paths already use * and + for their regex meanings.  Adding expressions 
as well overloads several characters so possibly requiring syntax to 
delimit an expression.

on behalf of the SPARQL Working Group

[2] http://www.w3.org/DesignIssues/N3Alternatives#Syntax

> On Tue, 2010-01-26 at 09:17 -0600, Dan Connolly wrote:
>> On Tue, 2010-01-26 at 12:39 +0100, Tim Berners-Lee wrote:
>>> Paths have been in N3 for a long time and much
>>> discussed.
>>> The characters used are "!" and "^".
>>> A discussion of the options is in
>>> http://www.w3.org/DesignIssues/N3Alternatives#Syntax
>>> It would be a really bad idea not to use the same punctuation in SPARQL.
>>> Could you pass that on?
>> As the message from Any shows, the WG is aware of N3 path syntax.
>> I'm not sure I agree N3 paths have been "much discussed",
>> and using / seems quite reasonable to me.
>>> Tim
>>> PS: Note also ^ is related to ^^ in that ^^ can be regarded
>>> as ^ if you want to reify datatypes -- to make an RDF
>>> system which uses only strings.
>>> On 2010-01 -22, at 22:10, Dan Connolly wrote:
>>>> The SPARQL WG is looking at paths...
>>>> http://www.w3.org/2009/sparql/docs/property-paths/Overview.xml
>>>> ... which is quite important for querying, e.g. lists:
>>>> select ?elt where {<alist>  rdf:rest*/rdf:first ?elt }
>>>> Meanwhile, they're using / where n3 uses ., I think.
>>>> They use ^ both as N3 uses it and to do the is/of thing.
>>>> They also include regex syntax such as +,*, ? and {n,m}
>>>> and ()s (but not for match groups).
>>>> It's pretty hard to argue against this in SPARQL; people
>>>> have been asking for it from the very start of the SPARQL
>>>> design.
>>>> Perhaps N3 should adapt in this direction?
>>>> The one place I'm inclined to push on is is/of; I'd
>>>> hate to lose that from N3. Though... with the @keywords
>>>> mechanism, maybe it's not so much of a conflict.
Received on Thursday, 25 February 2010 11:01:23 GMT

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