Re: SPARQL query result representation in Algebra

On 3/05/2011 07:43, Jitao Yang wrote:

> Do you know how to represent the SPARQL query result in Algebra?

Well, the point of any algebra is really to have a formal arithmetical 
expression that can be evaluated using rules of operation. In that 
sense, expressing a _result_ in an algebra is pointless, since the 
result is the outcome of the evaluation, not something that can be 
evaluated. The result is simply some collection of the terms that the 
algebra operates on.

Having said all that: the result of a SPARQL query is known as a 
solution sequence, which is formally defined as a (possibly unordered) 
list of solution mappings. Each solution mapping is a partial function 
from variables to RDF terms. A solution mapping can be written as m(?V 
-> t), mapping variable V to term t: { (V,t) }

So assuming we have the following query result:

?x	?y
=============
ex:a	ex:b
ex:c	ex:d

You could conceivably represent it in 'algebraic form' as follows:

[m_1(?x -> ex:a), m_1(?y -> ex:b), m_2(?x -> ex:c), m_2(?y -> ex:d)]

or more concisely, as :

[ {(x, ex:a), (y, ex:b)}, {(x, ex:c), (y, ex:d)} ]

Does that help?

Regards,

Jeen

Received on Tuesday, 3 May 2011 01:59:29 UTC