ER design problem

I'm trying to design a database and am having trouble with ER diagrams. The database will track record-of-calls.

Calls are made on a daily basis.
Each record-of-call corresponds to one project.

A different project may have unique attributes. For example,

project A has attributes projectID, region, customer_name
project B has attributes projectID, budget, region
project C has attributes projectID, business_type, number_of_deals
project D has attributes projectID, customer_name, business_type,

So, each call associated with project A must contain region, customer_name and projectID data.

Right now, the number of projects is stable (no increase or decrease in number of projects).
But, in the future, new projects may be added, although infrequently.

One suggestion was to have a Record_of_Calls Entity, a Projects Entity and a separate Project-Record_of_Calls entity for each project, because of different types and different number of attributes for each project. (i.e. a ProjectA-Record_of_Calls entity, ProjectB-Record_of_Calls entity, etc.)
Because with a single Project-Record_of_Calls entity, if a Project X has a unique attribute Y, not found in any other project, then, all other projects would have empty values for attribute Y (waste of space).

I am unsure that this is the best course of action.

Does anyone have any other suggestions?
Or perhaps some online resources to provide me with some guidance?

Thanks Received on Wed Feb 08 2006 - 22:25:57 CET