Thanks alot Charles.Your information was very useful for me.

I have some other questions:
1- first, I want to know how is it possible to change (or upgrade)
Structural methodologies (For Example SSADM or Oracle Case tools) in
implementing MIS projects to new methodologies , something like
Object Oriented methodologies and so on?how much risk and cost it
will contain?for more detail,I say that I'm working in a company that
implement Large scale MIS (Management Information System) projects.we
use Oracle as DataBase and its Case Tools for Analysis and design.We
have about 300 Oracle expert here that they trained with oracle tools
and they're working here almost 7-8 years.
Now the need for new methodologies is felt here in the company.I want
to know how can we handle this issue?

2-We use Oracle 6i now and as I mentioned above our company has
invested on Oracle tools and we can't change it.The other question is
about REUSE.Is it possible to have Reusability with Structral
methodologies Specially with support of Oracle?
and If we HAVE TO change our methodology how is it possible for a
company that has about 300 Oracle expert (Analyst and designer) to do
it?

Thanks alot,
Elham.