Unequal SPARQL algebras

[Jindřich Mynarz]

Hi,

I'm wondering why Jena thinks the optimized SPARQL algebras of the
following queries are different:

# Query 1
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>

SELECT *
WHERE {
  ?concept skos:broader [ skos:prefLabel ?broaderLabel ] .
}

# Query 1 algebra
(bgp
  (triple ?concept <http://www.w3.org/2004/02/skos/core#broader> ??0)
  (triple ??0 <http://www.w3.org/2004/02/skos/core#prefLabel> ?broaderLabel)
)

# Query 2
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>

SELECT *
WHERE {
  ?concept skos:broader/skos:prefLabel ?broaderLabel .
}

# Query 2 algebra
(bgp
  (triple ?concept <http://www.w3.org/2004/02/skos/core#broader> ??P4)
  (triple ??P4 <http://www.w3.org/2004/02/skos/core#prefLabel>
?broaderLabel)
)

When I compare if the query 1 algebra is equal to the query 2 algebra,
false is returned. However, the only difference I can spot between the
algebras is in the names of the non-distinguished variables ??0 and ??P4.
Why are the query algebras treated as different?

- Jindřich

-- 
Jindřich Mynarz
http://mynarz.net/#jindrich