Re: Navigation vs Relational operators
Date: 19 May 2004 08:36:09 -0700
Message-ID: <18c7b3c2.0405190736.38e59f6b_at_posting.google.com>
>> In what way is "navigation" different from using relational
operators? <<
Relational operators work on a set level. They can be applied in parallel to each element of the set all at once or in a non-determinisitic order. Navigational operations require an order of execution.
Example: In the nested set model of a tree, given one node, you can determine its superiors with a single predicate that can be applied to all the nodes at once to put them into the subset. Using a simple organizational chart:
SELECT O2.*
FROM OrgChart AS O1, OrgChart AS O2
WHERE O1.lft BETWEEN O2.lft AND O2.rgt
AND O1.emp = :myemployee;
In an adjacency list model, I have to start at the node and work my way up the tree to the root node. I cannot take a random node and apply a characteristic function to it. Received on Wed May 19 2004 - 17:36:09 CEST