Re: What databases have taught me

frebe73_at_gmail.com wrote:
> In fact, subtyping have to be used extremly carefully if you don't want
> to mess things up. It is a very inflexible tool.

Agreed - it's badly misunderstood, but is a poisonous pet even for the wise. Among other things, it's frequently treated as an implementation tool ("subclassing"), users ignore the need for subtypes to not restrict the precondition but fully deliver the postcondition (the former can be relaxed but not the latter)...

Mutation, of course, is a source of endless problems (hence the Circle/Elipse debate when you "change" the x or y), but is largely another variable/value debacle.  

• erk