In LDAP there are two common ways of grouping users.  The objectClass posixGroup and the objectClass groupofNames.  What’s the difference?
posixGroup:  Uses the memberUid attribute which contains only the value of the UID of a users full DN.  For example:
memberUID: someuser

groupofNames: Uses the member attribute which contains the full DN of the user.  For example:
member: uid=someuser,ou=People,dc=example,dc=com

The posixGroup version is generally use in UNIX environments.
The groupof Names version is the more Windows/AD like method.  EMC VNX Unisphere expects this method.