How do you model unbalanced hierarchies?

How do you model unbalanced hierarchies?

Post by Joe Dunca » Sun, 06 Feb 2000 04:00:00



How do you model hierarchies with multiple numbers of levels?

First example, an organization structure such as this:
CEO
  VP1
    DEPT1
       DEPT1A
           DEPT1AA
  VP2
    DEPT2
       DEPT2A

That is, some branches of the organization have more levels than others.

Second example, a budget category scheme with different numbers of upper
levels:
LEVEL1A (Top Level)
  LEVEL2A (Intermediate level, child of LEVEL1A)
     LEVEL3A (Bottom level, child of LEVEL2A)
  LEVEL2B (Top level, not a child of LEVEL1A)
    LEVEL3B (Bottom level, child of LEVEL2B)

--
Joseph Duncan
Daugherty Systems

 
 
 

How do you model unbalanced hierarchies?

Post by Brad Ais » Sun, 06 Feb 2000 04:00:00



> How do you model hierarchies with multiple numbers of levels?
> First example, an organization structure such as this:
> CEO
>   VP1
>     DEPT1
>        DEPT1A
>            DEPT1AA
>   VP2
>     DEPT2
>        DEPT2A

> That is, some branches of the organization have more levels than others.

> Second example, a budget category scheme with different numbers of upper
> levels:
> LEVEL1A (Top Level)
>   LEVEL2A (Intermediate level, child of LEVEL1A)
>      LEVEL3A (Bottom level, child of LEVEL2A)
>   LEVEL2B (Top level, not a child of LEVEL1A)
>     LEVEL3B (Bottom level, child of LEVEL2B)

You have a few options.

First, you can impose an artifical new hierarchy that is the same as the
deepest actual hierarchy. Then put "placeholder" members corresponding
to the higher levels, at the lower levels.

ex.

For above, you have an "AA" level -- so, for the "2" branch, just put
something like "<DEPT2A>" in the "AA" field, for leaf level members.
Thus, they will have "DEPT2A" in their [DEPT A] level, and "<DEPT2A>" in
their [DEPT AA] level. The "<" and ">" signify a pseudo level, when
browsing.

Another option, which you can use in conjunction with the first, is to
create two or more hierarchies, based on categories. You might have a
"top two levels" and "top three levels" etc. hierarchy, which do not try
to include the lower levels where there are some branches without level
members. Then, you can use those hierarchies to uniformly browse, albeit
without the lower levels in the cases where they exist.

Third, you can, in addition, make the lower level members in dimension
properties, and test for those in cases where it matters. You can also
add a property to each member, indicating the depth of actual levels,
thus indicating for any member, whether certain levels make sense.

--

http://www.brad-aisa.com/   -- PGP public key available at:
http://pgp.mit.edu:11371/pks/lookup?search=Brad+Aisa&op=index

"The paper wall will be next to fall." -- Brad Aisa

 
 
 

1. Unbalanced hierarchies in DW/OLAP


Ralph Kimball has a good discussion of RDBMS alternatives in his Sept/Oct 98
articles in DBMS magazine (http://www.dbmsmag.com) and in his new book, "The
Data Warehouse Lifecycle Toolkit".  

In general, multidimensional databases are much better at handling unbalanced
hierarchies than relational databases -- it's just not an problem with products
like Essbase, TM/1 or Gentia.  See the discussion of "Ragged Hierarchies"  in
Erik Thomsen's book, "OLAP Solutions".  

Steve Elkins
Technium

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