Entity sets - containment and parent-child

[Mark Beall]

On Nov 17, 2009, at 11:40 AM, Carl Ollivier-Gooch wrote:

> 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.

Right, sorry, I was thinking about the entity sets in the wrong way  
(somehow my brain was thinking that the switch_order argument would  
magically do this, but that's not what it does).

So then createAssociation(model,mesh) should create a entity-set  
relation and createAssociation(mesh,model) should create a different  
entity-entity relation. Of course, in our implementation, these are  
really just things that are pretending to be relations and entity  
sets, but that doesn't really matter.

If that's the case, it would seem you just need to ask for the right  
relation, not necessarily be able to change them from one type to  
another (in this case it's pretty equivalent, maybe not in other cases  
that I haven't thought of).

mark