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 - 06:15:10 CDT
