Here's a simple diagram of types derivation structure of object types related to user management:

acs_object ->
    party ->
        person ->
            user
        group
        relational_segment

• acs_object is the root object type in OpenACS.

• A party represents a set of one or more parties with an optional e-mail address.

• A person is a party with one member. This type stores first and last name information.

• A user is a person who has registered as an OpenACS user. This type store's the user's password and other relevant information.

• A group defines a set of parties. The parties are either users (who are related to the group using a membership relationship) or another group (related to the group by a composite relationship).

• A relational segment is a party that defines a subgroup of a group. This is a lightweight datatype used to model simple partitionings of the members of a group, i.e. students, professors, and teaching assistents in .LRN.