Re: Proving an Upgrade is Possible

Kenneth Downs wrote:
> If you have a data dictionary containing the meta data that describes the
> database, an upgrade = a change to the data dicitonary. So just as a user
> transaction changes the state of a database, an upgrade changes the meta
> data, or the meta state.

Ok. So you are talking about updates to the database schema.

> My goal is to always know completely whether all structure changes to a db
> are valid.

When you say "structure changes" you don't mean just changes to the structure, do you? You mean changes to both the database structure and the database constraints, right? Although below it seems you in fact exclude changes to the structure and only consider changes to the constraints.

> Here is a case of where you can prove an upgrade will fail, or at least you
> cannot prove it will succeed. If the WIDGETS table currently has a unique
> constraint on COL_A, COL_B, and COL_C, we know that an upgrade (or any
> change to the database) can fail if the new version has the unique
> constraint only on COL_A and COL_B. While it may succeed in some cases, it
> will fail in others.

Ok, so I suspect are you asking the following:

"Given the old database schema and a few updates to its constraints (but not its structure) is it possible to algorithmically decide (or mathematically prove) whether all instances of the old schema are also instances of the new schema?"

I leave it to you whether it is "algorithmically decide" or "mathematically prove".

Am I close?

• Jan Hidders