[squeak-dev] conceptual help please

Chris Cunnington smalltalktelevision at gmail.com
Wed Sep 12 01:24:48 UTC 2012

On 12-09-11 9:02 PM, Joseph J Alotta wrote:
> I think it would be like this:
> A (1) Family has (2) Clients who have (3) Accounts each having (4) Folios which contain (5) Securities.
> Should I implement this directly in a class hierarchy, even though each class is very different from the parent class?
I gave advice yesterday and got it backwards, but I figure I'll try 
again anyway.

I think you're answering your own question by saying "even though each 
class is very different from the parent". Doesn't sound like inheritance 
much, does it? Inheritance hierarchies start general and get more 
specific as they go down. Automobile --> car --> sedan --> Chevrolet --> 

Your five objects don't sound like they descend with increasing 
specificity. They do form a tree diagram in that they become more 
numerous as you descend. Your hierarchy is a "part-of", aggregation, 
whole-part, composite, or "has-a" hierarchy. (Thank you Chamond Liu from 
pg. 21 of "Smalltalk, Objects, And Design". 
). You start with one family and you end with it having many, many 
securities. The difference between inheritance and composition is a 
large topic, but this could be a start:


I can't say how you'd design your application, but it sounds like you 
already know inheritance won't be the relationship of those classes.

Hope That Helps,


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