Order of triple patterns in Where Clause

[Kashif Rabbani]

Hi awesome community,

I have a question,  I am working on optimizing SPARQL query plan and I wonder 
does the order of triple patterns in the where clause effects the query plan or 
not?

For example, given a following query:

PREFIX  bio:  <http://purl.org/vocab/bio/0.1/>
PREFIX  mo:   <http://purl.org/ontology/mo/>
PREFIX  mbz:  <http://dbtune.org/musicbrainz/resource/vocab/>
PREFIX  cmno: <http://purl.org/ontology/classicalmusicnav#>

SELECT  ?a ?b ?c
WHERE
  { ?a  mbz:alias           "Amy Beach" .
    ?b  cmno:hasInfluenced  ?a .
    ?c  mo:composer         ?b ;
        bio:date            ?d
  }



// Let’s generate its algebra
Op op = Algebra.compile(query); results into this:

(project (?a ?b ?c)
  (bgp
    (triple ?a <http://dbtune.org/musicbrainz/resource/vocab/alias> "Amy Beach")
    (triple ?b <http://purl.org/ontology/classicalmusicnav#hasInfluenced> ?a)
    (triple ?c <http://purl.org/ontology/mo/composer> ?b)
    (triple ?c <http://purl.org/vocab/bio/0.1/date> ?d)
  ))

The bgp in algebra follows the exact same order as specified in the where 
clause of the query. Very precisely, does Jena constructs the query plan as it 
is? or it will change the order at some other level?

I would be happy if someone can guide me about how the Jena's plan actually 
constructed. If I will use some statistics of the actual RDF graph to change 
the order of triple patterns in the BGP based on selectivity, would it optimize 
the plan somehow?

Many Thanks,


Best Regards,
Kashif Rabbani.