A thin GUI produced from evolutionary prototyping might be placed in front of a set of cooperating business objects derived from a business-object model. But prototyping alone is unlikely to produce a coherent design for business objects. These must be designed separately. Prototyping is not design.
A logical model is not design. It is abstract. A design needs to take into account the implementation environment. In Visual Basic 6 distributed development, the environment and potential impacts on other systems are complex. You need to adopt a benchmarking strategy to test and refine a design.
Data modeling is not design. Data modeling approaches to development assume that processing consists of simple inquiries and updates. GUI interfaces enable highly complex transactions to be built (for example, hierarchies and networks built as a single unit of work). The physical design to achieve performance and data integrity can be complex and can require separate modeling.
CASE tools do not guarantee good design. A mass of diagrams and dictionary prints can give the impression of detailed consideration. CASE tools improve productivity regardless of quality and talent, but they should be given only to those capable of doing the job without the tools. Few CASE tools provide adequate support for physical design. To do so, they would have to incorporate a model of the physical infrastructure and its performance characteristics.