Re: Use of the term "hierarchy"

Kenneth Downs wrote:
> Generally speaking, we seem to use the word hierarchy to mean a situation
> where a table has a foreign key to itself (or a child table has two foreign
> keys to the same table that are non-transitive), with the usual assumption
> that nesting could go to any level and that the levels are
> indistinguishable from each other.
>
> We don't tend to say hierarchy when referring to the structure of related
> tables, such as Jobs -> Orders -> Order Lines. This always looked like a
> hierarchy to me though. It is a hierarchy of unlike items, in which the
> allowed relationships of parent/child are determined by table structure.
>
> So if we have hierarchies of unlike items and then those of like items, it
> seems we may mistake one for the other.

Sure. We've been discussing this a lot. There was even a thread I started about a month ago called (IIRC) Three Kinds of Logical Trees.

http://groups.google.com/group/comp.databases.theory/browse_thread/thread/4278824e341371c5/c10c7a30c510531d

Since then, I've been referring to these as homogeneous trees, and static heterogeneous trees. There are also dynamic heterogeneous trees, like parse trees.

Marshall Received on Fri Aug 26 2005 - 03:17:06 CEST