SPARQL

Hello,

my name is André Bolles and I'm studying computer science in Oldenburg,
Germany. In the context of my diploma thesis I analysed the technical
report:

SPARQL Query Language for RDF

By doing this I think found some unclear parts in this document, so that
there may be some users who do not exactly know how to evaluate some
queries. I will tell you these parts and explain why I think these parts are
not clear.

1.
In the left join definition there is said the following:

LeftJoin(Ω1, Ω2, expr) =
    { merge(μ1, μ2) | μ1 in Ω1and μ2 in Ω2, and μ1 and μ2 are
compatible and expr(merge(μ1, μ2)) is true } set-union
    { μ1 | μ1 in Ω1and μ2 in Ω2, and μ1 and μ2 are not compatible }
set-union
    { μ1 | μ1 in Ω1and μ2 in Ω2, and μ1 and μ2 are compatible and
expr(merge(μ1, μ2)) is false }


But, what if there is no solution in Ω2. The sparql implementation in ARQ
says that in this case the solution from Ω1 will be taken, but this is not
said in the technical report.

2. There is said:

A solution mapping, μ, is a partial function μ : V -> T.

But what is T. I think you mean RDF-T.

3. The domain of μ, dom(μ), is the subset of V where μ is defined.

This is trivial, because dom(x) always defines the set, where x is defined.
This is the definition of dom.

Maybe these hints can be helpful by improving this recommendation.

Greetings,

Andre Bolles