Hi

I want to write an engine for processing SPARQL queries. i want to use jena to 
parse SPARQL queries and convert them to a internal form for my application. i 
can parse queries and convert them to query algebra using this code:

Query q=QueryFactory.create("select ?s ?o where {?s ?p ?o }");
Op op = Algebra.compile(q) ;

but i don't know how to use op and what is the uses of op.visit(opVisitor) .

in more detail: i want to convert query to a left deep tree and then process 
query operators in a pipelined manner.

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