More than one group for each user

[luiz@pucrs.br]

Hello

I´m sorry if this is a stupid question (and for my poor english), but I´m a
bit confused about the group attributions in LDAP.
I have some users that need to belong to more than one group, but I only
found the "gidNumber" attribute, for the primary group. Is there one
attribute for the secondary groups? Or the approaching to solve the problem
is different in LDAP? I´m thinking in UNIX terms...
Let me try to explain better.
For example: I need to create one SAMBA share for each discipline of our
educational intitution. The teacher of the discipline needs to map this
share. But Martin is the teacher of 5 disciplines. Actually, I was create
one Unix user and group for each discipline and added the user "martin" in
each group of each discipline. Like this:
disc1: martin
disc2: fred
disc3: martin
disc4: arthur
disc5: martin,arthur, franck
disc6: martin,carl
disc7: martin,jess
Then, I set SAMBA server to permit the login and the work of all members of
the group. There are also graduation students that belonging to some
research project, with a separeted share. Then, the student nees to map 2
or 3 different shares.
I didn´t understand how to make this using LDAP. :-(
Can anyone help me? I think it´s something very simple that I couldn´t see
in the docs...
Thank you very much to all.