Groups Design

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Essentials

User directory
Sitewide administrator directory
Subsite administrator directory
Tcl script directory
OpenACS 4 Groups Requirements
Data model
PL/SQL file
- community-core-create.sql
- groups-create.sql
ER diagram
Transaction flow diagram

Introduction

Almost all database-backed websites have users, and need to model the grouping of users. The OpenACS 4 Parties and Groups system is intended to provide the flexibility needed to model complex real-world organizational structures, particularly to support powerful subsite services; that is, where one OpenACS installation can support what appears to the user as distinct web services for different user communities.

Historical Considerations

The primary limitation of the OpenACS 3.x user group system is that it restricts the application developer to representing a "flat group" that contains only users: The user_groups table may contain the group_id of a parent group, but parent-child relationship support is limited because it only allows one kind of relationship between groups to be represented. Moreover, the Oracle database's limited support for tree-like structures makes the queries over these relationships expensive.

In addition, the Module Scoping design in OpenACS 3.0 introduced a party abstraction - a thing that is a person or a group of people - though not in the form of an explicit table. Rather, the triple of scope, user_id, and group_id columns was used to identify the party. One disadvantage of this design convention is that it increases a data model's complexity by requiring the programmer to:

add these three columns to each "scoped" table
define a multi-column check constraint to protect against data corruption (e.g., a row with a scope value of "group" but a null group_id)
perform extra checks in Tcl and PL/SQL functions and procedures to check both the user_id and group_id values

Competitive Analysis

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Design Tradeoffs

The core of the Group Systems data model is quite simple, but it was designed in the hopes of modeling "real world" organizations which can be complex graph structures. The Groups System only considers groups that can be modeled using directed acyclic graphs, but queries over these structures are still complex enough to slow the system down. Since almost every page will have at least one membership check, a number of triggers, views, and auxiliary tables have been created in the hopes of increasing performance. To keep the triggers simple and the number of triggers small, the data model disallows updates on the membership and composition tables, only inserts and deletes are permitted.

The data model has tried to balance the need to model actual organizations without making the system too complex or too slow. The added triggers, views, and tables and will increase storage requirements and the insert and delete times in an effort to speed access time. The limited flexibility (no updates on membership) trades against the complexity of the code.

Data Model Discussion

The Group System data model consists of the following tables:

parties: The set of all defined parties: any person, user, or group must have a corresponding row in this table.
persons: The set of all defined persons. To allow easy sorting of persons, the name requirement 30.10 is met by splitting the person's name into two columns: first_names and last_name.
users: The set of all registered users; this table includes information about the user's email address and the user's visits to the site.
user_preferences: Preferences for the user.
groups: The set of all defined groups.
group_types: When a new type of group is created, this table holds additional knowledge level attributes for the group and its subtypes.
membership_rels: The set of direct membership relationships between a group and a party.
group_member_index: A mapping of a party P to the groups {G_i }the party is a member of; this mapping includes the type of relationship by including the appropriaterel_id from the membership_rels table.
composition_rels: The set of direct component relationships between a group and another group.
group_component_index: A mapping of a group Gto the set of groups {G_i } that G is a component of; this mapping includes the type of relationship by including the appropriaterel_id from the composition_rels table.

New groups are created through the group.new constructor. When a specialized type of group is required, the group type can be extended by an application developer. Membership constraints can be specified at creation time by passing a parent group to the constructor.

The membership_rels and composition_rels tables indicate a group's direct members and direct components; these tables do not provide a record of the members or components that are in the group by virtue of being a member or component of one of the group's component groups. Site pages will query group membership often, but the network of component groups can become a very complex directed acyclic graph and traversing this graph for every query will quickly degrade performance. To make membership queries responsive, the data model includes triggers (described in the next paragraph) which watch for changes in membership or composition and update tables that maintain the group party mappings, i.e., group_member_index and group_component_index. One can think of these tables as a manually maintained index.

The following triggers keep the group_*_index tables up to date:

membership_rels_in_tr: Is executed when a new group/member relationship is created (an insert on membership_rels)
membership_rels_del_tr: Is executed when a group/member relationship is deleted (a delete on membership_rels)
composition_rels_in_tr: Is executed when a new group/component relationship is created (an insert on composition_rels)
composition_rels_del_tr: Is executed when a group/component relationship is deleted (a delete on composition_rels)

The data model provides the following views onto the group_member_index and group_component_index tables. No code outside of Groups System should modify the group_*_index tables.

group_member_map: A mapping of a party to the groups the party is a member of; this mapping includes the type of relationship by including the appropriaterel_id from the membership_rels table.
group_approved_member_map: A mapping of a party to the groups the party is an approved member of (member_state is 'approved'); this mapping includes the type of relationship by including the appropriaterel_id from the membership_rels table.
group_distinct_member_map: A person may appear in the group member map multiple times, for example, by being a member of two different groups that are both components of a third group. This view is strictly a mapping of approved members to groups.
group_component_map: A mapping of a group Gto the set of groups {G_i } group G is a component of; this mapping includes the type of relationship by including the appropriaterel_id from the composition_rels table.
party_member_map: A mapping of a party P to the set of parties {P_i } party P is a member of.
party_approved_member_map: A mapping of a party P to the set of parties {P_i } party P is an approved member of.

API

The API consists of tables and views and PL/SQL functions.

Tables and Views

The group_types table is used to create new types of groups.

The group_member_map, group_approved_member_map, group_distinct_member_map, group_component_map, party_member_map, and party_approved_member_map views are used to query group membership and composition.

PL/SQL API

Person

person.new creates a new person and returns the person_id. The function must be given the full name of the person in two pieces: first_names and last_name. All other fields are optional and default to null except for object_type which defaults to person and creation_date which defaults to sysdate. The interface for this function is:

function person.new (
  person_id          persons.person_id%TYPE,
  object_type        acs_objects.object_type%TYPE,
  creation_date      acs_objects.creation_date%TYPE,
  creation_user      acs_objects.creation_user%TYPE,
  creation_ip        acs_objects.creation_ip%TYPE,
  email              parties.email%TYPE,
  url                parties.url%TYPE,
  first_names        persons.first_names%TYPE,
  last_name          persons.last_name%TYPE
) return persons.person_id%TYPE;

person.delete deletes the person whose person_id is passed to it. The interface for this procedure is:

procedure person.delete (
  person_id     persons.person_id%TYPE
);

person.name returns the name of the person whose person_id is passed to it. The interface for this function is:

function person.name (
  person_id     persons.person_id%TYPE
) return varchar;

User

acs_user.new creates a new user and returns the user_id. The function must be given the user's email address and the full name of the user in two pieces: first_names and last_name. All other fields are optional. The interface for this function is:

function acs_user.new (
  user_id            users.user_id%TYPE,
  object_type        acs_objects.object_type%TYPE,
  creation_date      acs_objects.creation_date%TYPE,
  creation_user      acs_objects.creation_user%TYPE,
  creation_ip        acs_objects.creation_ip%TYPE,
  email              parties.email%TYPE,
  url                parties.url%TYPE,
  first_names        persons.first_names%TYPE,
  last_name          persons.last_name%TYPE
  password           users.password%TYPE,
  salt               users.salt%TYPE,
  password_question  users.password_question%TYPE,
  password_answer    users.password_answer%TYPE,
  screen_name        users.screen_name%TYPE,
  email_verified_p   users.email_verified_p%TYPE
) return users.user_id%TYPE;

acs_user.delete deletes the user whose user_id is passed to it. The interface for this procedure is:

procedure acs_user.delete (
  user_id       users.user_id%TYPE
);

Use the procedures acs_user.approve_email and acs_user.unapprove_email to specify whether the user's email address is valid. The interface for these procedures are:

procedure acs_user.approve_email (
  user_id       users.user_id%TYPE
);

procedure acs_user.unapprove_email (
  user_id       users.user_id%TYPE
);

Group

acs_group.new creates a new group and returns the group_id. All fields are optional and default to null except for object_type which defaults to 'group', creation_date which defaults to sysdate, and group_name which is required. The interface for this function is:

function acs_group.new (
  group_id           groups.group_id%TYPE,
  object_type        acs_objects.object_type%TYPE,
  creation_date      acs_objects.creation_date%TYPE,
  creation_user      acs_objects.creation_user%TYPE,
  creation_ip        acs_objects.creation_ip%TYPE,
  email              parties.email%TYPE,
  url                parties.url%TYPE,
  group_name         groups.group_name%TYPE
) return groups.group_id%TYPE;

acs_group.name returns the name of the group whose group_id is passed to it. The interface for this function is:

function acs_group.name (
  group_id      groups.group_id%TYPE
) return varchar;

acs_group.member_p returns 't' if the specified party is a member of the specified group. Returns 'f' otherwise. The interface for this function is:

function acs_group.member_p (
  group_id      groups.group_id%TYPE,
  party_id      parties.party_id%TYPE,
) return char;

Membership Relationship

membership_rel.new creates a new membership relationship type between two parties and returns the relationship type's rel_id. All fields are optional and default to null except for rel_type which defaults to membership_rel. The interface for this function is:

function membership_rel.new (
  rel_id             membership_rels.rel_id%TYPE,
  rel_type           acs_rels.rel_type%TYPE,
  object_id_one      acs_rels.object_id_one%TYPE,
  object_id_two      acs_rels.object_id_two%TYPE,
  member_state       membership_rels.member_state%TYPE,
  creation_user      acs_objects.creation_user%TYPE,
  creation_ip        acs_objects.creation_ip%TYPE,
) return membership_rels.rel_id%TYPE;

membership_rel.ban sets the member_state of the given rel_id to 'banned'. The interface for this procedure is:

procedure membership_rel.ban (
  rel_id           membership_rels.rel_id%TYPE
);

membership_rel.approve sets the member_state of the given rel_id to 'approved'. The interface for this procedure is:

procedure membership_rel.approve (
  rel_id           membership_rels.rel_id%TYPE
);

membership_rel.reject sets the member_state of the given rel_id to 'rejected. The interface for this procedure is:

procedure membership_rel.reject (
  rel_id           membership_rels.rel_id%TYPE
);

membership_rel.unapprove sets the member_state of the given rel_id to an empty string ''. The interface for this procedure is:

procedure membership_rel.unapprove (
  rel_id           membership_rels.rel_id%TYPE
);

membership_rel.deleted sets the member_state of the given rel_id to 'deleted'. The interface for this procedure is:

procedure membership_rel.deleted (
  rel_id           membership_rels.rel_id%TYPE
);

membership_rel.delete deletes the given rel_id. The interface for this procedure is:

procedure membership_rel.delete (
  rel_id           membership_rels.rel_id%TYPE
);

Composition Relationship

composition_rel.new creates a new composition relationship type and returns the relationship's rel_id. All fields are optional and default to null except for rel_type which defaults to composition_rel. The interface for this function is:

function membership_rel.new (
  rel_id             composition_rels.rel_id%TYPE,
  rel_type           acs_rels.rel_type%TYPE,
  object_id_one      acs_rels.object_id_one%TYPE,
  object_id_two      acs_rels.object_id_two%TYPE,
  creation_user      acs_objects.creation_user%TYPE,
  creation_ip        acs_objects.creation_ip%TYPE,
) return composition_rels.rel_id%TYPE;

composition_rel.delete deletes the given rel_id. The interface for this procedure is:

procedure membership_rel.delete (
  rel_id           composition_rels.rel_id%TYPE
);

User Interface

Describe the admin pages.

Configuration/Parameters

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Acceptance Tests

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Future Improvements/Areas of Likely Change

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Authors

System creator: Rafael H. Schloming
System owner: Rafael H. Schloming
Documentation author: Mark Thomas

Revision History

Document Revision #	Action Taken, Notes	When?	By Whom?
0.1	Creation	08/22/2000	Rafael H. Schloming
0.2	Initial Revision	08/30/2000	Mark Thomas
0.3	Additional revisions; tried to clarify membership/compostion	09/08/2000	Mark Thomas