strawberry wrote:
> In some hierarchichal models a root parent is simply one without
> ancestors, i.e. where `parent` is null. Similarly an EV dose can
> simply be described as a dose with a NULL infusion time. The 'waste of
> space' you describe is trivial. So, purely on the information
> provided, I'd be tempted to go with this model.


Thanks to both responses. All I really need to do is just set the
infusion field to null for EV doses.

> There is a danger that
> an incomplete entry for an IV dose might be misinterpreted as an EV
> dose, but I think this could be handled through the data input
> interface and judicious use of the DEFAULT setting

This doesn't pose a problem as long it is only my software accessng the
database. My EV dose class will throw an exception if you try to get the
infusion time from it, and my IV class has a default infusionTime of 0.

Thanks again.

Lionel.