Implementations using "compositional semantics"

Hello,

In a recent paper about "Semantics and Complexity in 
SPARQL" (http://www.dcc.uchile.cl/~cgutierr/ftp/sparql-ext.pdf) Perez et.al. 
mention two approaches to compute solutions for graph patterns - one using a 
procedural semantics and another using a compositional semantics. As a real 
implementation for the first they name Jena's ARQ. I'm interested in an 
implementation following the second approach. Does someone, familiar with the 
paper, know of any?
-- 
Bye,
Ole
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