What is the BDB logic model

Question

when the Native XML DB access the xml document will thought a logic model to mapping the record.
What is the BDB logic model?? is a tree model ??
A
/ | \
B C D
or node just link first-child and other child link each other??
and when the path is A/D,will first get "A" first child, and sequence search "D"
A
B-C-D

Answer 1

Hi Henry,
I'm afraid I'm finding it a little difficult to understand what you're asking. I'll try to answer, but feel free to ask more specific questions.
With the 2.3 release, DB XML moved from the first model you described to the second model. That is, DB XML used to have links to all an elements children in the element itself, but now it only contains first child (and last child) pointers.
We made this change because of what we know internally as the hundred thousand child problem - which is a common pattern that we see where people have one top level element with a very large (and usually increasing) number of child elements arranged in a shallow tree. This situation resulted in a very large number of child pointers being stored in one place, causing unmarshalling to be very slow whenever that element was accessed.
How we navigate the path "A/D" depends a lot on whether there is an index present that we can use. In the case where there isn't an index, the scenario is as you described, and the child list is walked using first child/next sibling links.
I hope this helps,
John