Entity sets - containment and parent-child

[Carl Ollivier-Gooch]

Mark Beall wrote:

>> In most cases you can support either, and which one you want depends 
>> on the usage.  I think this would be far more useful though if there 
>> were a function to change the type of relation dynamically.  
>> Requesting an entity-set type be changed to an entity-both type, and 
>> back again, for smoothing, is the easiest use case for this, but 
>> adaptive refinement is another good example.
> 
> I don't think I understand why you would want to change the relation. If 
> I have classification as an entity-set relation, why would I want it 
> differently. I will say that I'm assuming that iRel_getEntEntAssociation 
> always allows you to efficiently query the relation in either direction 
> (this is implied due to the existence of the "switch_order" argument).

Here's an example:  Suppose you're doing swapping, or any other 
topological modification to a mesh.  Chances are excellent that you only 
want to do the 2-2 swap on the surface if both surface faces classify on 
the same model face.  Now, if you've got an entity-entity relation 
giving you classification, that's an easy test.  On the other hand, if 
you've got a geometric entity-mesh set relation, you have to find out 
which set a mesh face is in, which can only be done through an 
exhaustive search of faces.  So the higher memory (e-e) relation is much 
lower CPU.

Carl

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