Re: Agenda for June 14 Telcon - Revision 1

On 14 Jun 2011, at 15:19, Eric Prud'hommeaux <eric@w3.org> wrote:

> Not making assertions *is* the standard RDF way of dealing with missing information. There is no rdf:NULL. 

I guess we all know that.

> We don't know or care about the difference between NULL and a non-existent value

You don't care, but in SQL there is a huge difference. As a matter of fact in SQL you can model both and they would behave in different ways. And the data we are talking about does come from SQL RDBs.

> (nor does SQL, for that matter).

FALSE. I already argued that SQL can represent both absence of information (in the same way as your DM: new pseudo-binary property plus a foreign key as the rsf:type) and NULL values with their peculiar distinct semantics and behaviour.

> 
> Given a relation R with a attributes, compose a query:
>  "SELECT " + ("?" + a₁) … + ("?" + aₐ)
> + "WHERE { _:s a <" + R + ">"
> + "          ; <" + R + "#" + a₁ + "> ?" + a₁
> + "          ; <" + R + "#" + aₐ + "> ?" + aₐ
> + "      }"
> 
> Conctacts Example:
>  Table:              SPARQL Query:                           Result:
> ┌┤Contacts├──────┐  SELECT ?name ?company                    ┌────────────────┐
> │ name │ company │  WHERE { _:s a <Contacts>                 │  who │ company │
> ├──────┼─────────┤            ; <Contacts#name> ?name        ├──────┼─────────┤
> │  Bob │   BobCo │            ; <Contacts#company ?company   │  Bob │   BobCo │
> │  Sue │    NULL │        }                                  │  Sue │ UNBOUND │
> └──────┴─────────┘                                           └──────┴─────────┘
> 
> No information is lost. NULL is no longer spelled "NULL", but instead as a lack of a binding. Applications using SPARQL interpret this lack of a binding the same way applications using SQL interpret NULL.

As I said several times, this confuses the presence of a NULL value with the absence of any value. So this can not be a general solution.

--e.

Received on Tuesday, 14 June 2011 14:58:55 UTC