Persisting Data For A Pluggable Tree

Hi all,

I am rather new to database design and modelling concepts in general
and was hoping for some advice on a problem I am trying to solve. I
have designed a piece of software that creates a tree with pluggable
nodes. Each node class can have 0 to n distinct classes plugged into
it to define the type for that node.

For example, a node plugged with a 'customer' class and an 'engineer'
class would indicate that this node in the tree is an engineer who is
also a customer. We could also have a 'owner', 'engineer' etc.

I now want to persist this tree in an SQL Server 2000 Database. I have
chosen to implement the nested set model, and have thought about the
following table design:

table NODE_TABLE:
lft INTEGER
rft INTEGER
propsID INTEGER

table PROPERTIES_TABLE:
propsID INTEGER
tableName VARCHAR

table CUSTOMER_TABLE:
propsID INTEGER
firstname CHAR
lastname CHAR

table ENGINEER_TABLE:
propsID INTEGER
num_completed_projects INTEGER
degree CHAR
school CHAR

table OWNER_TABLE:
propsID INTEGER
companyName CHAR

So, given the above example - I would have a NODE_TABLE that links to 2
entries in PROPERTIES_TABLE. One entry would link to an entry in the
CUSTOMER_TABLE, the other to an entry in ENGINEER_TABLE.

Are there any more efficient solutions to this problem? As i said, I
am very new to DB design and would welcome any feedback or suggestions
of how else I might model my pluggable tree in a Database. Thank you,

Bob Yohan