Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

Alexandr Savinov wrote:
> But this example was used to demonstrate that
> tables are used to represent some entities from the problem domain and
> in this sense it is possible to model the problem domain by using
> tables.

Keep in mind that relations also "model" relationships, not just "entities." They are predicates, which of course vary infinitely; data design is the process of deciding the types of facts with which your application needs to concern itself.

> Some consequences of such a definition can be found on
> conceptoriented.com (not all - many things are not described).

Some advice for your FAQs: I found them very difficult to get through because of the sheer number of nouns, and inconsistent (or opaque) usage. If nothing else, the volume of distinct nouns swamps any attempt to understand them (at least for me).

Here's a partial list: concept, entity, space, collection, set, combination, primitive concept, dimension, variable, domain, value, item, characteristic, coordinate, reference, custom reference, group, constraint, part, representation, description. There are many more, and verbs and adjectives too, and none of it helps describe much to me beyond the 4th page. You might want some "semantics" - e.g. algebraic definitions, a glossary, something. I think fewer words might be better than what you have.

> In relational model tables are simply containers (collection of other
> entities) and it is impossible to directly define new properties for
> them.

Every relation (not table - use that when discussing SQL, for clarity) is defined by the designer. What properties are you talking about?

> Records are simply objects (combinations of other entities) and we
> cannot add records to records. And such a definition is really effective
> and covers a huge number of situations.

Just because it covers "a huge number of situations" doesn't mean other methods don't cover those same situations, and better. Relations do.

> However, the question was how
> can we treat tables as entities and can they be treated as entities at
> all.

What does "entity" mean, and why is it valuable to treat X as one?

> There was an opinion that tables are not entities and have nothing
> to do with the data semantics.

Relations define the data - of course it's semantic.

> As far as I understand the relational model does not use any system
> table or a table of tables - it is how RDBMSs are implemented.
> Relational model works independently of how this meta information is
> stored and if it exists at all.

True, relational doesn't directly address the situation, but no theoretical extension is needed - just, perhaps, a standard schema for the system relations.

• erk