Re: a union is always a join!

paul c wrote:

>I just want to comment on one point, users can think whatever they
>want (when they away from the desk as it were), but when they are
>operating the db, the only view they should take is that of the
>intentions of the data design. If the design doesn't concern itself
>with recording changes (as opposed to the result of recording
>changes), eg., if the design doesn't handle 'before' and 'after', then
>a user who concerns himself with that is a mystic!

You are confusing two things.

1. The fact that updates to relational databases are possible, that users need to be aware of what updates are possible and what they will mean when they happen. This is just a matter of understanding the intentions of the data design, as you put it.
2. The fact that a database may explicitly store information about past states of affairs, by design, and that it is impossible to obtain, from the *present* database state, information about a past state of affairs if that information isn't retained by design. This is obvious, and it's not what the disagreement is about.

>Obviously a data design is just a mechanical reflection of one or more
>chosen abstractions of reality. All mystics should make a vow to
>remember daily what McCarthy said about submarines trying to swim.

Obviously, windmills are a technological innovation that helped upset the social order of the feudal world. Don Quixote may have been crazy, but his windmills and his fight were real. Your mystics are figments of your imagination.

-- 
Reinier