Re: Nulls, integrity, the closed world assumption and events

Jonathan Leffler wrote:
> David wrote:
> > Whilst on the subject of nulls, I have seen a paper written in '83
> > by Carlo Zaniolo that suggests nulls can represent "no information"
> > (which encompasses all the more specific interpretations such as
> > "unknown" and "non-existent"), and this appears to lead to a
> > decent mathematical model, unlike Codd's 3vl which is far from
> > compelling.
>
> Can you identify this paper more precisely? Is it this one:
>
> The database language GEM, Carlo Zaniolo, May 1983, ACM SIGMOD Record,
> Proceedings of the 1983 ACM SIGMOD international conference on
> Management of data SIGMOD '83, Volume 13 Issue 4
>
> GEM (an acronym for General Entity Manipulator) is a general-purpose
> query and update language for the DSIS data model, which is a semantic
> data model of the Entity-Relationship type. GEM is designed as an
> easy-to-use extension of the relational language QUEL, providing support
> for the notions of entities with surrogates, aggregation,
> generalization, null values, and set-valued attributes.

C. Zaniolo. Database Relations with Null Values. Journal of Computer and System Sciences, 28:142--166, 1984.
http://citeseer.ist.psu.edu/zaniolo84database.html Received on Sun Jan 14 2007 - 02:20:09 CET