Directory servers that follow the directory information model have no restrictions on whether an attribute can appear twice in the database. Distinguished Names, however, must be unique. Some directory servers have a notion of attribute uniqueness, which, if enabled, would enforce the uniqueness of certain configured attributes, meaning that when such enforcement is configured, for example, for the attribute
employeeNumber, the following could not occur (in the same database):
The above is a clumsy attempt to make an employee a member of two organizations. If uniqueness of the
employeeNumber attribute (which in this case is a component of the distinguished name) is not enforced, then the above DNs become possible, though hardly advisable since better methods exist to establish membership of organizations.
There is nothing to prevent employees from being stored twice in your database, and this is a common occurrence and depends entirely on the data model used by the organization.