On May 7, 2008, at 1:46 PM, Robert Walker wrote:
Vertical or horizontal? With vertical this will still select on
the root, won't it?
That's actually a good question. It will have to select against the
root, obviously, to pick up those attributes, but I don't think it
then calls all the other siblings if you call against a leaf node,
but I could be wrong about that.
No, it won't. I was just clarifying that it will still do two selects
to retrieve one EO.
I think it has a similar performance hit as a one-to-many
relationship when accessing leaf node. But, if you call the root
node I thought it would then access the entire tree, which can be
really bad.
Yeah, it goes "select crazy" when you do that.
Chuck
On May 7, 2008, at 4:27 PM, Chuck Hill wrote:
On May 7, 2008, at 1:14 PM, Robert Walker wrote:
Agreed,
The only time vertical inheritance makes sense if when you always
fetch against leaf nodes of the inheritance tree and only if the
inheritance tree is very shallow. Take that to mean one level deep
of inheritance with an abstract root entity that you never fetch
against.
Anything more complex than that I would recommend single-table.
My 2 cents.
Vertical or horizontal? With vertical this will still select on
the root, won't it?
Chuck
On May 7, 2008, at 3:54 PM, Chuck Hill wrote:
On May 7, 2008, at 12:48 PM, Florijan Stamenkovic wrote:
Hi all,
In the "[slightly OT] data modeling question" there is some talk
of drawbacks of inheritance, specifically of vertical
inheritance... Since I am currently contemplating implementing a
reasonably complex system, and have thought of using vertical
inheritance, this has got me worried. So, what's the deal???
My situation: a structure of over 10 entities (15ish),
inheritance up to 4 levels in depth. The amount of records per
entity will be quite small (ranging from 5 - maybe 30), so I do
not worry about performance. Many operations will be defined on
the topmost entity. Relationships will almost always relate to
the topmost entity, which will be abstract. I might want to
define additional subentities in the future. Subentities will
have a sufficient amount of their own properties to discourage
me from single table inheritance. Horizontal might do, I do not
think I will be changing the existing structure once made.
I've never done inheritance till now. Am I going to commit
suicide over this?
You might want to check for suicide exclusions in your life
insurance policy. :-) David Avendasora was using Vertical with
JC. He stopped. Maybe he can provide some pointers. My advice
would be to ignore that "Subentities will have a sufficient
amount of their own properties" and use Single Table. Or,
failing that, Horizontal. Vertical is the least efficient and
the least used hence has a higher probability of bugs.
Chuck
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