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Re: Converting VALUES to SPARQL algebra

From: Andy Seaborne <andy@apache.org>
Date: Mon, 02 Mar 2015 17:11:18 +0000
Message-ID: <54F499B6.3000904@apache.org>
To: public-sparql-dev@w3.org
On 02/03/15 11:53, Joachim Van Herwegen wrote:
> My problem is actually more of a syntax problem: I want to know what the
> exact SPARQL algebra syntax is when converting one of these queries, I
> understand what they are supposed to do but I don't know how to write it
> in algebra format.
> As mentioned before, I find examples using table/row, but I don't think
> these are part of the spec?

They are not part of the spec.  There isn't a formal syntax for the 
SPARQL algebra.

Also, there isn't a completely formal defintion of the abstract syntax 
tree (AST) and so the mapping from AST to algebra is not as formal as it 
might be.  SPARQL 1.0 simply didn't have the time nor the energy to do 
it.  Retrofitting at 1.1 was too much like disturbance to the existing 
spec and the message was zero, or minimal, change to 1.0 in the 1.1 work.

The translation text is:
"""
is formed by forming a solution mapping from the variable in the 
corresponding position in list of variables (or single variable), 
omitting a binding if the BindingValue is the word UNDEF.
"""

If you take a reasonably direct choice of the AST from the grammar, you 
get a variables and then values lined up with the variables.  ARQ 
happens to call those "tables".

The best thing is for suggestions for better wording to be sent here 
because they are logged and would be picked up by any future working group.

	Andy
Received on Monday, 2 March 2015 17:11:55 UTC

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