Is there a way to "restrict" the tree structure

[Dan Shriver <dshriver@sharemedia.com>]

Hello,
     I was wondering if it is possible to put restrictions on
the LDAP tree structure (to force it that objects of type A can
only live under objects of type B and C...), and likewise to
specify that parts of the tree structure will be (whatever) and
cannot be modified.
     I have not seen any mention of such capabilities and kind
of doubt they exist.
    Also does specifying an object attribute to be "single
valued" still cause problems?  I saw mention on the list of this
restriction causing difficulties.