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Re: Comments on 2.1.4 "Syntax for blank nodes" in 6 April 2006 CR

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Mon, 24 Jul 2006 10:03:40 +0100
Message-ID: <44C48CEC.8050807@hp.com>
To: Fred Zemke <fred.zemke@oracle.com>
CC: public-rdf-dawg@w3.org

Fred Zemke wrote:
> 2.1.4 Syntax for blank nodes

> It says "Blank nodes...will take part in the pattern matching".
> There are no examples of how pattern matching with SPARQL
> blank nodes works.  Section 2.5.4 "Basic graph patterns in SPARQL
> syntax" gives an example of the syntax only, but does not discuss
> the semantics of the example that it presents.  Section 2.8.3
> "Blank nodes" and 2.8.4 "RDF collections" show how the abbreviations
> are expanded into SPARQL blank nodes, but do not show how the
> expanded patterns behave either.

This becomes "3.1.4 Syntax for Blank Nodes" in rq24.  Section 3 is just
about syntax so how blank nodes behaves is dealt with new section
"5 Basic Graph Patterns".

> 2.1.4 Syntax for blank nodes
> The preceding section 2.1.3 "Syntax for variables" says
> "Variables in SPARQL have global scope".

Now section "3.1.3 Syntax for Query Variables" and it is about the ? form.
Blank nodes have variable characteristics through entailment.  For some forms
of entailment, blank nodes can be treated as variables.

> Section 2.8.3 "blank nodes"

Now "3.1.4 Syntax for Blank Nodes"

> says "Blank nodes have labels which are scoped to the query".  
> It is not clear to me what the difference between the "global scope"
> of a variable vs. being "scoped to the query" means in practice.
> At any rate, I think it would be good to state the scope of blank
> nodes (or what I prefer to call blank node identifiers)
> in section 2.1.4, as a parallelism with 2.1.3, and possibly
> harmonize the terminology.

Blank nodes are indicated by either the label form "_:a" or by use of "[ ]".
Blank node labels are written as "_:a" for a blank node with label "a" and the
label is scoped to the basic graph pattern.

> Fred
Received on Monday, 24 July 2006 09:03:56 UTC

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