Thomas Beale wrote: > Kerry Raymond wrote: > >> If I might ask a rather mundane technical question about archetypes ... >> >> Looking at the archetype models, there appears to be no way to enforce >> that the class to be used for some specific piece of information is >> exactly that class and not one of its subtypes. For example, what if >> it is important to have a DVTime used and not a DVPartialTime? Or an >> ObjectRef that should never an AccessGroupRef or a PartyRef? >> >> My feeling is that the class constraint in an archetype needs an >> additional property "subtypesAllowed" or similar to cater for the two >> cases. > > > Hi Kerry, > > there are two ways to see this. The orthodox oo modelling approach is to > say: if your model defines X (concrete) as a subtype of Y (also > concrete) then at runtime, an X is always acceptable in a variable of > type Y. By this argument, archetypes should not try to circumvent this.
What I am wondering now is during automated object creation process, it has to be clear which concrete class to be instantiated - either X or Y ? Apparently the end user will not supply the class name to the system ;) My guess is that the choice has to be made before 'operational' archetypes are created based on some extra input from local settings, for instance a localized template. > If on the other hand, there are circumsances where a Y is ok but not an > X, then the underlying reference model should say so by modelling X and > Y as disjoint subtypes of a common parent W. > > A pragmatic approach would be to do what you say. We could probably > argue for this just on the basis of the fact that many reference models > (i.e. object models) are not well constructed, and out of the control of > the archetype designers, and/or that models consdered good today are > shown up later on by changing requirements, which changes the validity > of inheritances such as the one Kerry points out. > > The purist in me says stick with the first way of seeing it; the realist > says to consider the second. What do others think? > > - thomas beale > > - > If you have any questions about using this list, > please send a message to d.lloyd at openehr.org > - If you have any questions about using this list, please send a message to d.lloyd at openehr.org
