[Developers] Hierarchical included types

[Scott Meyer]

Philip Kendall wrote:
> Is the client designed to support "hierarchical" included types?
> 
> The situation I've just noticed is that:
> 
> * Sports Facility has Structure as an included type
> * Structure has Project Focus as an included type
> 
> However, using the client to add Sports Facility to a topic results in
> only Sports Facility and Structure being added to the topic, not Project
> Focus.
> 
> Is this a bug in the client, or should Project Focus be added as an
> included type of Sports Facility?

It is intentional that the client asserts only immediately included
types. Project Focus should be added as an included type of Sports Facility.

Our experience has been that a traditional deep inheritance hierarchy
is surprisingly fragile over time and, since the graph structure of
the data makes no demands on "object layout", delivers very little
benefit over simple type inclusion or co-typing.

-Scott