Re: What does this NULL mean?


>When we
>are talking about catalogs and (conventional) databases then the
>situation is the same. In principle, they can be viewed as one database.
>However, they are at different levels so it is more appropriate to apply
>different representation and manipulation methods for them (which do not
>exist).

A clear non sequitur. Like Paul said, there is an evident leverage if
the schema can be managed like any other database.

>> A relvar attribute is deleted in case of no integrity constraints
>> violation.

>Right. But who said that it should happen?

The catalog's designer.

> I, as a developer of this
>database, did not say that.

As a developer you are a catalog's user, and users don't dictate the
rules.

> It happens because some anonimous developer
>of this concrete DBMS implemented it so. I cannot influence this
>bechaviou because it is hard coded. It is not part of my model. It is
>not part of my database. It is part of catalog hard-coded bahvior.

Just the same as your database for your users.

> This
>is only one example that catalog does not strictly obey to the normal
>laws of user-defined data.

I see a very strict obedience, only the roles change.

>Yes. And apply any concrete data model including RM to the problem of
>global data management (catalogs, meta-info etc.) is also not very
>appropriate.

Why not?

What is the alternative?

The Hierarchical Model?

Catalogs, meta-info, etc are data like any other. They don't have
anything in special.

>You simply create a new database using tools provided by
>another database. For example, I could create a complex multi-level
>system using Oracle. But the main problem is that Oracle database is
>unaware what kind of system it manages. It thinks that it is relational
>model while in reality it is something different. Instead, we need to
>have a theory or a model that would allow us to create such multi-level
>data models.

You are missing the point. You don't have to create anything. The
catalog design is a part of the DBMS implementation, and the developers
don't have to design their own catalogs.

What you could do is to design a better DBMS than Oracle.

>Yes, of course we can apply RM to any data. But as I already mentioned
>above, this model will be unaware that the data it represents has much
>more complex meaning and hence it will not be able to help us in
>managing this data. In this case we need to implement most of complex
>issues ourselves. That is not the best way and hence the conclusion
>could be that we need something new.

I don't see any sense here. Any DBMS is completely unaware of the
meaning of the data. DBMS only can check consistency and to perform
symbolic manipulation.


Regards
Alfredo

.

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