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

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.

-- 
Jonathan Leffler                   #include <disclaimer.h>
Email: jleffler_at_earthlink.net, jleffler_at_us.ibm.com
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