Re: The Theoretical Foundations of the Relational Model

In article <3D168294.C823240E_at_managesoft.com>, Clifford Heath <cjh_nospam_at_managesoft.com> wrote:
>
>I brought up the Laws of Form because GSB begins with the concept of
>distinction (as opposed to identity), and rebuilds the whole of Boolean
>logic around a single operator, in a system requiring only two axioms, not
>the five(?) of first-order logic. I'm not a mathematician, but his algebra
>of distinction is remarkably simple and enlightening.

Well, he limits himself to monadic first order logic, so that is bound to be simpeler than full first order logic. :-)

>To my mind, the OO practitioner's insistence on disembodied identity is an
>attempt to record that some things are believed to be distinct, even though
>we might not yet be able to codify the distinction. In any case there will
>be a need to distinguish things, but we can delay defining the distinction.
>In other words, we can delay codifying our understanding.

OTOH, the assumption in the RM that everything can be identified by its direct attributes is IMO rather strong. In fact, we know for sure that it is too strong because that is why we have something called Weak Entities. Also for Relationships it doesn't really hold because when mapping them to relations we have to "add" the primary keys of the entities that the relationship holds between in order to get enough attributes for a primary key. However choosing a primary key is actually an implementation decision that should not belong in a logical data model.

• Jan Hidders