Special-ness of root set: Impl. vs. data model

[Jason Kraftcheck]

On 08/31/2010 12:20 AM, Mark Miller wrote:
> On Mon, 2010-08-30 at 19:59, Tim Tautges wrote:
>> On 08/27/2010 02:37 PM, Miller, Mark C. wrote:
>>>
>> I think this is a case where full generality of the data model
>> conflicts with usability of the interface, where here I 
>> define that as restricting what you can do with/on the root set.
> 
> I am not sure where '...full generality...' is really coming in here.
> The data model is the data model. The root set is a) a set and b) the
> universe set. There is nothing I am doing/suggesting to 'generalize' the
> data model. I am merely asking that the root set, since it is a set, be
> allowed to be used as a set in ALL instances where a set is involved and
> where it make sense at the data model level. I am asking for an
> interpretation of the root set in the iMesh API that is 'free' from
> implementation details.
> 

I think I disagree with both of you (Mark and Tim) on one important aspect
of this:  the root set is not part of the data model.  The data model has:
the mesh, elements, vertices, entity sets, and tags on any of those.  The
root set is a fiction in the API to allow a) specifying either the entire
mesh or an entity set to query functions and b) used to indicate the mesh
when interacting with tags.  It is not, nor was it ever intended to be, a
proper set in the sense of the data model.  It is a convenience in the API
to avoid the need to have separate versions of many functions that act on
the mesh rather than a subset of the mesh.

- jason