Re: Joining data tables and system tables

> list all relations (tables) in database,
> together with total number of tuples (rows) in each relation.
> from a theoretical viewpoint.

An experimental db intened for ai applications has some parallels to your question. The db consists of things. The ultimate ancestor of everything in the db is named 'thing'. From 'thing' one can programmatically traverse all remaining things in the db. Each thing has a link to all references(->) to it.
In the example below, a programmer can retrieve that thing1 has 3 relationships.

thing1

thing5 = (->thing2 ->relatorX ->thing1)
thing6 = (->thing3 ->relatorY ->thing1)
thing7 = (->thing4 ->relatorZ ->thing1)

Although thing1 is related to 3 other things(2,3,4), this does not necessarily imply that thing1 is related to 3 "tables". For example if the relationships were:

thing5 = (->maxSize ->isPropOf ->thing1)
thing6 = (->person ->isA ->thing1)
thing7 = (->color ->isA ->thing1)

Then, in this case thing1 is related to only two things (person and color)
which are similar to "tables".

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