Re: database design method

Lauri Pietarinen wrote:
>Jan Hidders wrote:
>> Can you point me to the exact and complete definition of *the* language
>> in which you define constraints in the RM?
>
>"The Third Manifesto" by Date&Darwen defines a set of languages called "D"
>that are able to define arbitrary constraints. The same book defines
>"Tutorial-D", a sample language that has not been implemented.

Is this set of languages really a set in the sense that there is a proper definition of it in set theory? Or is there just a set of properties that should hold for the language (in which case it might be a class rather then a set). That sounds a bit as if there is not really such a thing as "the language in which you specify constraints in the RM". So how should I then understand Leandro's claim that in this language (which one) you can express every machine-enforceable constraint? Anyway, is there a proof somewhere that Tutorial-D is computationally complete?

>Dataphor "D4" belongs to "D", so I would say that "D4" is _a_ language
>in which you can define constraints.

Ok. Can I express that relation R2 is the transitive closure of relation R1?

• Jan Hidders