| Prev | Chapter 15. Kernel Documentation | Next |
|---|
By Rafael H. Schloming and Mark Thomas
=======User directory
Sitewide administrator directory
Subsite administrator directory
TCL script directory
Data model
PL/SQL file
ER diagram
Transaction flow diagram
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.
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
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.
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
{Gi}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
{Gi} 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
{Gi} 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 {Pi} party P is a member of.
party_approved_member_map
A mapping of a party P to the set of parties {Pi} party P is an approved member of.
The API consists of tables and views and PL/SQL functions.
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.
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 );
acs_user.receives_alerts_p returns 't' if the user should
receive email alerts and 'f' otherwise. The interface for this
function is:
function acs_user.receives_alerts_p ( user_id users.user_id%TYPE ) return varchar;
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 );
Mark Thomas
| 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 |