Re: double linked list

>> It's not important whether TC is built on the fly (for example,
with "recursive with" construct), or incrementally maintained. <<

I grant that once you have the transitive closure, a lot of problems are easy. But building it and storing each possible path as a separate row, is expensive.

>> I don't follow here. <<

In a nested set model, the (lft, rgt) pairs are ordered, so I have a left-most (oldest) child, a right-most (youngest) child and an ordering of the sibling in between.

>> Once again, it is implementation dependent in the sence that the
user is
locked into a particular labeling schema. <<

Okay. The phrase "implementation dependent" is used in ANSI/ISO Standards to mean that the vendor gets to determine something about a feature.

>> there only one adjacency list model. <<

Two.

              Albert 
            /        \
          /            \
        Bert         Chuck 
                   /    |   \
                 /      |     \
               /        |       \
             /          |         \
        Donna        Eddie        Fred 

 CREATE TABLE Parent_Down_Tree
 (parent_id CHAR (8), -- null means child is the root   child_id CHAR(8) NOT NULL);

 parent child

  NULL     'Albert' 
 'Albert'  'Bert'   
 'Bert'    'Chuck'
 'Chuck'   'Donna' 
 'Chuck    'Eddie'
 'Chuck'   'Fred' 

 CREATE TABLE Child_Up_Tree
 (parent_id CHAR (8) NOT NULL,
  child_id CHAR(8)); -- null means child is a leaf

 parent child

 'Albert'  'Chuck'
 'Albert'  'Bert'   
 'Bert'     NULL'
 'Donna'    NULL
 'Eddie'    NULL
 'Fred'     NULL

>> It is more general too. <<

True.

>> That might be correct. However, until Herarchy Theory in the
Relational Model is mostly undeveloped I prefer not to dismiss alternative solutions easily. <<

And I am a "Standards Faniac" <g> ... Received on Sun Feb 09 2003 - 20:35:53 CST