Entity sets - containment and parent-child

[Mark Beall]

OK. However, I could do the same thing with two entity sets. In your  
first example, I could use one to describe the mesh classified on the  
model face and another to describe the mesh on the boundary of the  
model face. If I modify your example a bit to include another division  
of the mesh on the model face, say, a partitioning of it, then I need  
another entity set anyhow. Essentially having the parent-child  
relationship gives you some, but not all, of the functionality of  
another entity set in that one set.

Two other questions that your answer brings up:

1) If you want to decompose your "model face" set into multiple  
subsets, wouldn't it be best to have the iterators on entity sets be  
capable of doing a "deep" traversal of the entity set (returning all  
of entities in the entity set, even if they are contained in a entity  
set contained in the entity set). It would seem that if entity sets  
are going to be used in the way you describe, everyone would have to  
write that code anyhow since they don't know what they will be given.

2) Has anyone defined how entity sets would be used to describe the  
relation between a mesh and a model? Since there is more than one  
possible way to do that (you add the mesh of the edge around a face as  
children of the entity set for the mesh face and I add them as entity  
sets in the entity set for the mesh face), it would seem that it needs  
to be defined otherwise no one will be able to write code that uses  
that information.


On Nov 12, 2009, at 12:36 PM, Tim Tautges wrote:

> I figured you'd ask that next.  The two that come to mind most  
> readily:
>
> a) I use entity sets to represent geometric topology groupings in  
> the mesh, and parent/child relations between those to represent the  
> topological relationships between the original geometric entities.   
> So, I have "model face" sets, whose contents are the mesh owned by  
> that model face, and children corresponding to the bounding model  
> edges.  Instead of directly including the mesh faces in a model face  
> set, say I want to preserve a grouping of those faces, e.g. the  
> original rectangles of faces composing an "E" or "L" shaped  
> structured mesh.  This would most naturally be stored as rectangle  
> sets of faces contained in the model face set.  Similar examples can  
> be made for swept meshes in 3d.
>
> b) Parts in a parallel mesh: parent-child relations can be used to  
> represent the relationship between parts and their boundaries.  If  
> you construct a partition using e.g. material sets or model volume  
> sets, then a part set will have both child sets (the boundaries of  
> the part) and contained sets (the model volumes composing the part).
>
> - tim
>
> Mark Beall wrote:
>> I'd be interested in knowing the various use cases for using entity  
>> set containment vs. a parent-child relationship. It seems to me  
>> that they are just about identical, so I'm curious when one would  
>> use one vs. the other.
>> mark
>
> -- 
> ================================================================
> "You will keep in perfect peace him whose mind is
>  steadfast, because he trusts in you."               Isaiah 26:3
>
>             Tim Tautges            Argonne National Laboratory
>         (tautges at mcs.anl.gov)      (telecommuting from UW-Madison)
>         phone: (608) 263-8485      1500 Engineering Dr.
>           fax: (608) 263-4499      Madison, WI 53706
>