Re: Mixing OO and DB

"Brian Selzer" <brian_at_selzer-software.com> wrote in message news:XDCBj.22735$R84.448_at_newssvr25.news.prodigy.net...

> I'll buy that a schema can be part of multiple applications, but that
there
> can be multiple ways to represent the same information does not alter what
> information is to be and can be recorded. I can represent a point in
space
> by using Cartesian coordinates or by using polar coordinates, but it is
> still the same point; in the same way, schemata are equivalent if exactly
> the same information that can be represented in a database with one schema
> can be represented in a database with another schema. Equivalent schemata
> can be derived from one another, relegating whether any particular
relation
> is a base relation or a derived relation to being an implementation
matter.
> But what is important and what cannot be decoupled from the application is
> what information is to be and can be recorded. That is what a schema
> specifies, and without that there is no point in even having an
application.

This is true, but it overlooks an important consideration. When multiple applications manipulate or retrieve data in a database, each application typically interacts with only part of the schema. To the application, it appears as if the subschema that it interacts with were the entire schema.

It isn't until you take a database centered viewpoint that you begin to assess the entire schema from an information point of view.

In fact, it's an oversimplification to say that the schema is "part of" multiple applications.

An analogous thing happens when a single application interacts with multiple databases. Received on Wed Mar 12 2008 - 11:45:15 CET