Auto-generated SPARQL Algebra expressions for the algebra test suites

Attached is a first shot at a script which serializes parsed SPARQL back
into Algebra expressions similar to the (informative) syntax used in the
specification.  I have only eyeballed it, but some caveats:

* It doesn't serialize FILTERs
* The parser breaks up triple patterns in a BGP into Joins against each
triple pattern

So:  BGP([(?s,?p,?o),(?s2,?p2,?o2)]
becomes: Join(BGP([(?s,?p,?o),]),BGP([(?s2,?p2,?o2)])

Otherwise, everything else should be okay.  I wanted to make sure this
is what we have in mind and that the expressions being generated are not
malformed before turning it loose on the entire test collection.

-- 
Chimezie Ogbuji
Lead Systems Analyst
Thoracic and Cardiovascular Surgery
Cleveland Clinic Foundation
9500 Euclid Avenue/ W26
Cleveland, Ohio 44195
Office: (216)444-8593
ogbujic@ccf.org


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## Filter-placement - 2 (data-r2/algebra/filter-placement-2.rq) ##
PREFIX : <http://example/>

SELECT ?v 
{ 
    FILTER (?v = 2)
    ?s :p ?v . 
}

Join(BGP(),BGP((?s, rdflib.URIRef('http://example/p'), ?v)))
##########################

## Filter-nested - 1 (data-r2/algebra/filter-nested-1.rq) ##
PREFIX : <http://example/> 

SELECT ?v
{ :x :p ?v . FILTER(?v = 1) }

BGP((rdflib.URIRef('http://example/x'), rdflib.URIRef('http://example/p'), ?v))
#######################

## Filter-placement - 3 (data-r2/algebra/filter-placement-3.rq) ##
PREFIX : <http://example/>

SELECT ?v ?w
{ 
    FILTER (?v = 2)
    FILTER (?w = 3)
    ?s :p ?v . 
    ?s :q ?w .
}

Join(Join(BGP(),BGP()),BGP((?s, rdflib.URIRef('http://example/p'), ?v),(?s, rdflib.URIRef('http://example/q'), ?w)))
##########################

## Filter-scope - 1 (data-r2/algebra/filter-scope-1.rq) ##
PREFIX :    <http://example/>

SELECT *
{ 
    :x :p ?v . 
    { :x :q ?w 
      OPTIONAL {  :x :p ?v2 FILTER(?v = 1) }
    }
}

BGP((rdflib.URIRef('http://example/x'), rdflib.URIRef('http://example/p'), ?v))
######################

## Optional-filter - scope of variable (data-r2/algebra/opt-filter-3.rq) ##
PREFIX :    <http://example/>

SELECT *
{ 
    :x :p ?v . 
    { :x :q ?w 
      # ?v is not in scope so ?v2 never set
      OPTIONAL {  :x :p ?v2 FILTER(?v = 1) }
    }
}

BGP((rdflib.URIRef('http://example/x'), rdflib.URIRef('http://example/p'), ?v))
#########################################

## Filter-placement - 1 (data-r2/algebra/filter-placement-1.rq) ##
PREFIX : <http://example/>

SELECT ?v 
{ 
    ?s :p ?v . 
    FILTER (?v = 2)
}

BGP((?s, rdflib.URIRef('http://example/p'), ?v))
##########################

## Optional-filter - 2 filters (data-r2/algebra/opt-filter-2.rq) ##
PREFIX :    <http://example/>

SELECT *
{ 
  ?x :p ?v .
  OPTIONAL
  { 
    ?y :q ?w .
    FILTER(?v=2)
    FILTER(?w=3)
  }
}

LeftJoin(BGP((?x, rdflib.URIRef('http://example/p'), ?v)),Join(BGP((?y, rdflib.URIRef('http://example/q'), ?w)),BGP()))
#################################

## Join scope - 1 (data-r2/algebra/var-scope-join-1.rq) ##
PREFIX : <http://example/>

SELECT *
{ 
  ?X  :name "paul"
  {?Y :name "george" . OPTIONAL { ?X :email ?Z } }
}


BGP((?X, rdflib.URIRef('http://example/name'), rdflib.Literal('paul', lang=None, datatype=None)))
####################

## Filter-nested - 2 (data-r2/algebra/filter-nested-2.rq) ##
PREFIX : <http://example/> 

SELECT ?v
{ :x :p ?v . { FILTER(?v = 1) } }

BGP((rdflib.URIRef('http://example/x'), rdflib.URIRef('http://example/p'), ?v))
#######################

## Nested Optionals - 2 (data-r2/algebra/two-nested-opt-alt.rq) ##
PREFIX :    <http://example/>

## The nested optional example, rewritten to a form that is the same
## for the SPARQL algebra and the declarative semantics.
SELECT *
{ 
    :x1 :p ?v .
    OPTIONAL { :x3 :q ?w }
    OPTIONAL { :x3 :q ?w  . :x2 :p ?v }
}

LeftJoin(LeftJoin(BGP((rdflib.URIRef('http://example/x1'), rdflib.URIRef('http://example/p'), ?v)),BGP((rdflib.URIRef('http://example/x3'), rdflib.URIRef('http://example/q'), ?w))),Join(BGP((rdflib.URIRef('http://example/x3'), rdflib.URIRef('http://example/q'), ?w)),BGP((rdflib.URIRef('http://example/x2'), rdflib.URIRef('http://example/p'), ?v))))
##########################

## Optional-filter - 1 (data-r2/algebra/opt-filter-1.rq) ##
PREFIX :    <http://example/>

SELECT *
{ 
  ?x :p ?v .
  OPTIONAL
  { 
    ?y :q ?w .
    FILTER(?v=2)
  }
}

LeftJoin(BGP((?x, rdflib.URIRef('http://example/p'), ?v)),BGP((?y, rdflib.URIRef('http://example/q'), ?w)))
#########################

## Nested Optionals - 1 (data-r2/algebra/two-nested-opt.rq) ##
PREFIX :    <http://example/>

SELECT *
{ 
    :x1 :p ?v .
    OPTIONAL
    {
      :x3 :q ?w .
      OPTIONAL { :x2 :p ?v }
    }
}

LeftJoin(BGP((rdflib.URIRef('http://example/x1'), rdflib.URIRef('http://example/p'), ?v)),LeftJoin(BGP((rdflib.URIRef('http://example/x3'), rdflib.URIRef('http://example/q'), ?w)),BGP((rdflib.URIRef('http://example/x2'), rdflib.URIRef('http://example/p'), ?v))))
##########################