Changing Field Type with Fields Editor in D2

Hi, I'm in trouble with the definition of a data field from the
field editor. In Delphi 2.01 there is an option the allows you to
define a persistent field with a type different from the database
type. If you want, you can replace TIntegerField with a TSmallIntField (see the
Database Application Developer's Guide, page 81). This could be useful
when you write a database independent application. I tried with a
dataset to change a field type but delphi gives me an error whenever
i set the Active property to TRUE.

Could you please help me ?

Thanks in advance,

David -