# SPARQL

From: Andre Bolles <Andre.Bolles@Informatik.Uni-Oldenburg.DE>
Date: Fri, 18 Jan 2008 09:00:28 +0100

Message-ID: <2C1FAA0701F94CA2911119EDB8281324@lgPC>
```
Hello,

my name is Andr¨¦ 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(¦¸1, ¦¸2, expr) =
{ merge(¦̀1, ¦̀2) | ¦̀1 in ¦¸1and ¦̀2 in ¦¸2, and ¦̀1 and ¦̀2 are
compatible and expr(merge(¦̀1, ¦̀2)) is true } set-union
{ ¦̀1 | ¦̀1 in ¦¸1and ¦̀2 in ¦¸2, and ¦̀1 and ¦̀2 are not compatible }
set-union
{ ¦̀1 | ¦̀1 in ¦¸1and ¦̀2 in ¦¸2, and ¦̀1 and ¦̀2 are compatible and
expr(merge(¦̀1, ¦̀2)) is false }

But, what if there is no solution in ¦¸2. The sparql implementation in ARQ
says that in this case the solution from ¦¸1 will be taken, but this is not
said in the technical report.

2. There is said:

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

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

3. The domain of ¦̀, dom(¦̀), is the subset of V where ¦̀ 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
```
Received on Friday, 18 January 2008 18:11:43 UTC

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