Re: domain questionnaire

David Cressey wrote:
>
> The question about Codd's requirement that meta data be stored in the
> same kind of structures as data makes me think of a lower level
> issue:
>
> I've seen this done in two ways.
>
> The first is to have multiple schemas in a database. One of the
> schemas is "SYSTEM", or some such name, and the meta data is stored
> in there, for all the schemas (including itself).
>
> The second is to have a collection of tables with reserved names,
> such as "RDB$RELATIONS" in every schema.
>
> My preference is for the first of these two choices. But what are
> the pros and cons of each of the two choices?

At first sight I would say the following:

• The advantage of the first way is that you can easily ask queries over all the meta-data of all the databases, even if you don't know their names.
• The advantage of the second way is that all meta-data of one database is grouped into a set of tables where you will find only information of this database.

A DBMS might in principle even offer both approaches by using the first way plus offering default views as in the second way.

-- 
  Jan Hidders