Re: Interesting article: In the Beginning: An RDBMS history

paul c wrote:
Jon Heggland wrote:
paul c wrote:
I'm darned if I know what a "relationship between tables" is unless
it's another table.

In my experience, it's rather common to use that phrase for foreign keys.

In a 'standard' that people rely on to make exact decisions, what good
is it to use it that way?

Who knows? My impression of the SQL standard's quality, clarity and
consistency isn't very favourable. I'm not saying that that is the
correct interpretation of the phrase in this case, just that it is a
possibility.

Wouldn't it be better to say exactly what it
is, for example, one projection is a subset of the other?

Perhaps, if that is what they mean. That is not completely equivalent to
a foreign key in the normal sense of the term, though.

For that matter, I don't know what the sql standard
would mean by "table" (assuming it uses that word). I've assumed that
it doesn't stand for a relation partly because it allows duplicates and
nulls. Without those differences, I imagine an sql table still couldn't
stand for any relation we choose because at least when I was using it
ten or more years ago a row-column intersection contained only a single
value, ie. some relations can't be expressed as one table.

Hm?

For sure, any single-rva-attribute relation, maybe others too.

Ok. I would say that a relation value *is* a single value, but I don't
want another fruitless 1NF debate. :) I'd rephrase your argument to say
that an sql table can't stand for any relvar we choose because SQL
doesn't support arbitrary user-defined types. Anyway, I would think that
"table" is one of the terms the SQL standard defines (implicitly or
explicitly), but I can't say for sure.
--
Jon
.

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