Re: vehicle to autoparts relationships
Date: Wed, 22 Nov 2006 22:34:15 GMT
Message-ID: <Hf49h.23630$cz.357862_at_ursa-nb00s0.nbnet.nb.ca>
Vadim Tropashko wrote:
>>Anybody noticed an implicit hierarchy of nested sets yet?
>
>
> Nested Sets
> ^^^^^^^^^^^^^^
> Another approach to a tree structure is modeling it as nested sets
>
> A
> .|
> ..---- B
> .|......|
> .|.......------ C
> .|......|
> .|.......------ D
> .|
> ..---- E
>
> Figure 5.2a: A tree.
>
> { { [C] [D] } { [E] } }
>
> Figure 5.2b: Nested sets structure for the tree at fig. 5.2a. Set
> elements are boxes, and sets are the ovals including them. Every parent
> set contains its children sets. (This is ASCII adaptation of the
> figure, of course)
>
>
> Clearly set containment can clearly accommodate any tree. Whenever we
> need to grow a tree by adding a new child, we just nest one more set
> into the appropriate parent set.
>
> A naive nested sets implementation would materialize a set of elements
> at each node. Aside from the fact that the RDBMS of your choice have
> has to be capable of operating on sets on the datatype level , this
> implementation would be quite inefficient. Every time a node is
> inserted into a tree, the chain of all the containing sets should be
> expanded to include (at least) one more element.
>
> A more sophisticated variant of Nested Sets has been widely popularized
> by Joe Celko. The main idea behind this encoding is representing nested
> sets as intervals of integers...
How does nested sets handle the part that is a part of multiple assemblies? Received on Wed Nov 22 2006 - 23:34:15 CET