[Zope] Abstract ZClasses and containing classes

Scenario: here is a hierarchy of ZClasses. AbsDogPoundOrganization - abstract class ForProfitOrganization - subclass of AbsDogPoundOrganization NonProfitOrganization - subclass of AbsDogPoundOrganization Now I want AbsDogPoundOrganization to contain the class of Location (not an abstract class). First, what is the correct way to define an abstract ZClass. Do you make one that has no constructors? The problem I see is that then the subclasses of AbsDogPoundOrganization don't allow me to create instances of Location within them.