Re: Information Preserving and ISSUE-42


On Wed, May 18, 2011 at 2:30 AM, Enrico Franconi <>wrote:

> On 18 May 2011, at 06:59, Juan Sequeda wrote:
> > So does that mean that you would translate all NULL values to a triple
> with rdb2rdf:NULL? That makes sense and would make the current direct
> mapping information preserving.
> Definitely not.
> Take the case of a RDB with a Person table, having ID, name, and age.
> If you query (in SQL with a simple conjunctive query) all the people with
> the same age of a specific person in the table having a NULL value as age,
> you do *not* get the people whose age is a NULL value. However, with your
> naive translation in RDF of this database, you would get the wrong answer
> with the same query translated in SPARQL.

Yes, if you have a query like the one you are stating. But for the direct
mapping, the input is the complete table. So it shouldn't be a problem...

> cheers
> --e.

Received on Wednesday, 18 May 2011 13:33:58 UTC