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Re: Why blank nodes?

From: Eric Prud'hommeaux <eric@w3.org>
Date: Fri, 7 Sep 2012 07:47:26 -0400
To: Steve Harris <steve.harris@garlik.com>
Cc: Antoine Zimmermann <antoine.zimmermann@emse.fr>, "public-rdf-wg@w3.org WG" <public-rdf-wg@w3.org>
Message-ID: <20120907114723.GC7520@w3.org>
* Steve Harris <steve.harris@garlik.com> [2012-09-07 12:08+0100]
> On 2012-09-07, at 11:41, Antoine Zimmermann wrote:
> 
> > Le 07/09/2012 12:35, Steve Harris a écrit :
> >> Taking a step back, and thinking about what we (Experian) actually use bNodes for, to inform our position on the various scope questions.
> >> 
> >> Basically, it's just a replacement for auto_increment columns in SQL.
> >> 
> >> There are two motivations for this
> >> 
> >> 1) it saves the data generating process from minting a globally unique identifier for it
> >> 2) it's more efficient in the store, as there's no need to store a text symbol for it
> >> 
> >> This has been helped by Skolem URIs, as now we have an easy way to refer to them between SPARQL queries.
> >> 
> >> Any other features of bNodes are just a distraction or inconvenience really.
> >> 
> >> I'm sure other people have different reasons for using them, anyone care to share?
> > 
> > 
> > Bnodes are an absolute requirement for OWL to be serialised in RDF. Without bnodes, it would be impossible to define an RDF-based semantics for OWL which is (mostly) compatible with the direct semantics.
> 
> What feature of bNodes makes the true though - that's what I was trying to get to.
> 
> > Bnodes are very often used to express n-ary relations.
> 
> Yup, for reasons 1) and 2) above, IMHO.

and 3) it's better not to utter an identifier which you can't or don't intend to honor in the future.
Sometimes that emerges from 1) or 2), but some data sources offer data which simply can't be repeatably discriminated, repeated rows in a database for example.

> > rdf:List without bnodes would be insane.
> 
> Right, that's mostly a syntactic thing.
> 
> - Steve
> 
> -- 
> Steve Harris, CTO
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> 

-- 
-ericP
Received on Friday, 7 September 2012 11:47:56 GMT

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