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Re: Blank node identifiers in FILTER clauses

From: Bijan Parsia <bparsia@cs.man.ac.uk>
Date: Wed, 28 Jun 2006 16:35:09 +0100
Message-Id: <2693D80C-67C2-4946-9898-B535AA283ED6@cs.man.ac.uk>
Cc: Jeen Broekstra <jeen@aduna.biz>, RDF Data Access Working Group <public-rdf-dawg@w3.org>
To: Kendall Clark <kendall@monkeyfist.com>

On Jun 28, 2006, at 1:32 PM, Kendall Clark wrote:

> On Jun 28, 2006, at 5:15 AM, Jeen Broekstra wrote:
>> I can live with either of these and have a slight preference for the
>> second. To be honest I could live without the blank nodes in queries
>> altogether. They are confusing and annoying (this discussion is a  
>> case
>> in point), and I find the supposed 'cut&paste' benefit  
>> unconvincing. But
>> that station is passed I guess.
> I couldn't agree more. I wasn't convinced by it as a reason,  
> offered by TimBL, for turtleizing our syntax, and I'm even less
> convinced by it now. It's the biggest single wart on SPARQL and I  
> wish we could chop it off w/out mercy.
> But I'm also not convinced that it's too late. If the WG decides to  
> do it, and will put in the work to make it happen,
> then it's "merely" a matter of doing the work.

I would like to separate the syntax issue from the capability issue.  
At the moment, as I understand it, BNodes in the query represent  
*undistinguished* variables, that is, variables that do not need a  
binding to a constant and *cannot* report their bindings (thus don't  
need to establish one). This is an important capability (distinct  
from projection) which currently there is no other way to (exactly)  
express in SPARQL.

On the other hand, since we can have BNodes in *answers*, we have a  
way for expression what one might called "semi-distinguished"  
variables, since normal variables aren't truly distinguished. In that  
case, I suppose projection *does* have the same effect as non- 
distinguished variables (since, if you know you are going to project  
away the variable, you don't *need* to examine the particular values  
for it).

It would be good for this all to be clearly expressed in the text.

Received on Wednesday, 28 June 2006 15:34:56 UTC

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