Re: Why bother with Logical data model?

Why? Because it saves time--perhaps not initially, but definitely in the long run. In most of the databases I've worked with there is a disparity between the logical model and the physical model. The logical model should at a minimum be in BCNF, but if possible, 5NF, but that is not always true in the physical model. Sometimes tables must be split for valid business reasons, such as security. Sometimes, though seldom, a denormalized table performs better--at least for the particular application where it is most used. The logical model should remain independent of such considerations, so that you can focus on the structure of the data that is to be stored--the domains, attributes, relations and constraints that need to be realized in order to satisfy the information requirements set down in the specification. Once you have a logical model, it is usually a simple matter to map it onto an implementation, taking into account at that time those other non-information related requirements. (Maybe you should get a better tool.) A logical model with many relations could go through dozens of iterations before it meets the information requirements, and the danger of the "Just Start Coding" approach is the temptation to start writing application code before the model is fixed. I've been called in on projects where a flawed or absent logical model required a major rewrite of several applications in order to resolve the numerous problems that existed. Code that masked the symptoms of the problems had to be removed, and then much of the core of the applications had to be rewritten in order to eliminate the problems, more than doubling the cost and causing the schedule to slip. Needless to say, the people who originally designed those systems had to find new jobs. It takes a lot more time and costs a lot more to clean up a mess than to prevent one

"Broons Bane" <newsgrouper_at_yahoo.com> wrote in message news:1155113261.739611.6280_at_h48g2000cwc.googlegroups.com...
> I'm working on a project where the logical data model stage slows the
> process down. I'm not talking about thinking time, that is always there
> as part of the process. I suppose the tool doesn't help. Oracle
> Designer is just awful and you spend an awful lot of time changing the
> tables and indexes generated by the logical model, where it would have
> been easier to go straight to table design in the first place.
>
> Now, I know part of the problem here is the tool I'm using.
>
> Has anybody had similar experiences or have any comments
>
Received on Wed Aug 09 2006 - 13:15:10 CEST