Re: Database schema for univesal usage

Kenneth Downs wrote:
> lauri.pietarinen_at_atbusiness.com wrote:
> >
> > What I am saying is that there are many degrees of flexibility that can
> > be built into the schema. Maybe we currently need only two different
> > kinds of phone nubmers, but we suspect that the situation might change
> > in the future. Should we go for the flexible schema now or just add
> > new columns into the table when we happen to need them? How will the
> > application programs be affected? How will the queries be affected?
> > Will generalising now unnecessarily complicate queries?
>
> As I said above, if you know that your toolkit does not handle schema
> changes well, then you are in trouble no matter what. If you provide extra
> stuff you have to constrain its use, and then you work harder making a UI
> for a structure that may not even be necessary. Balance this against the
> expense of adding things after the fact and they usually come out even in
> practice.
>
> What solves all of these cases is the ability to modify structure and
> corresponding code at low cost as the system evolves. Then you can have
> everything fit all of the time.

I actually agree with your viewpoint and I personally tend to design databases that are tightly fit. And it might indeed be the "app environment tail" wagging the "database model dog" that makes companies consider generic schemas (I am still calling them generic as opposed to spesific). If it costs $$$ to add a new column to a table then you propably start thinking in those terms.
I recently attended a Dama meeting where Len Silverston gave a presentation on his "Universal Data Models", which tend towards generic solutions. I confronted him on the issue of the database losing meaning via generalisation and he said that one of the motivations was indeed the expence of, say, adding a new column to an existing system. His presentation was well given and very informative and he does deserve to be listened to.

Being an advocate of tight db-models I have aquainted my self with Dataphor and Versata, both which take a slightly different approach to the application generation problem directly from the db-schema. Have I understood correctly that you have created some kind of similar product or in-house solution?

Regards,
Lauri Pietarinen Received on Wed May 25 2005 - 05:00:38 CEST