| Prev | Chapter�11.�Development Reference | Next |
|---|
+ +
by Vadim Nasardinov. Modified and converted to Docbook XML by Roberto Mello -
The code has been modified since this document was written so it is now out of date. See this forum thread.
Who
- (grantee_id) can do what
- (privilege) on which object
- (object_id).
-
+
The code has been modified since this document was written so it is now out of date. See this forum thread.
Who + (grantee_id) can do what + (privilege) on which object + (object_id). +
The general permissions system has a flexible (and relatively complex) data model in OpenACS. Developers who have not had the time to learn the internals of the data model may end up writing seemingly correct code that crashes their system in @@ -18,11 +19,11 @@ system internals.
In OpenACS, most of the interesting tables are expected to extend (subtype)
- the acs_objects table, i.e. they are expected to have an integer
- primary key column that references the object_id column of
- acs_objects.
+ the acs_objects table, i.e. they are expected to have an integer
+ primary key column that references the object_id column of
+ acs_objects.
-create table acs_objects ( +create table acs_objects ( object_id integer not null constraint acs_objects_pk primary key, @@ -46,23 +47,23 @@ );
This means that items that want to use the features of the
- OpenACS object system needs to have an entry in the acs_objects. This
+ OpenACS object system needs to have an entry in the acs_objects. This
allows developers to define relationships between any two entities A
and B by defining a relationship between their corresponding entries
- in the acs_objects table. One of the applications of this
+ in the acs_objects table. One of the applications of this
powerful capability is the general permissions system.
- At the heart of the permission system are two tables: acs_privileges
- and acs_permissions.
+ At the heart of the permission system are two tables: acs_privileges
+ and acs_permissions.
- create table acs_privileges ( + create table acs_privileges ( privilege varchar2(100) not null constraint acs_privileges_pk primary key, pretty_name varchar2(100), pretty_plural varchar2(100) );
- create table acs_permissions ( + create table acs_permissions ( object_id not null constraint acs_permissions_on_what_id_fk references acs_objects (object_id), @@ -76,14 +77,14 @@ primary key (object_id, grantee_id, privilege) );
- The acs_privileges table stores
+ The acs_privileges table stores
named privileges like read,
write, delete, create, and
- admin. The acs_permissions
+ admin. The acs_permissions
table stores assertions of the form:
- Who (grantee_id) can do what (privilege)
- on which object (object_id).
+ Who (grantee_id) can do what (privilege)
+ on which object (object_id).
The micromanaging approach to system security would be to require application developers to store permission information explicitly about every object, i.e. if the system has 100,000 and 1,000 users @@ -101,44 +102,26 @@ necessity to explicitly maintain security information for every single object. There are three kinds of hierarchies involved. These are discussed in the following sections. -
Suppose objects A, B, ..., and F form the following hierarchy. -
Table�11.2.�Context Hierarchy Example
|
- A
-
- | ||
|
- B
-
- |
- C
-
- | |
|
- D
-
- |
- E
-
- |
- F
-
- |
+
Table�10.2.�Context Hierarchy Example
| A + object_id=10 + | ||
| B + object_id=20 + | C + object_id=30 + | |
| D + object_id=40 + | E + object_id=50 + | F + object_id=60 + |
This can be represented in the acs_objects table by the following entries: -
+
The first entry tells us that object 20 is the descendant of object 10, and
the third entry shows that object 40 is the descendant of object 20. By
running a CONNECT BY query,
@@ -164,9 +147,9 @@
Despite its potentially great storage costs, maintaining a
flattened representation of the context tree is exactly what OpenACS
does. The flattened context tree is stored in the
- acs_object_context_index table.
+ acs_object_context_index table.
- create table acs_object_context_index ( + create table acs_object_context_index ( object_id not null constraint acs_obj_context_idx_obj_id_fk references acs_objects (object_id), @@ -184,12 +167,12 @@ an index-organized table, which means it is substantially optimized for access by primary key. Number two, as the above computations suggest, the size of the table - grows polynomially + grows polynomially with respect to the average number of descendants that an object - has, and exponentially + has, and exponentially with respect to the depth of the context tree.- The
acs_object_context_indexis kept in sync with the + The acs_object_context_index is kept in sync with the acs_objects table by triggers like this:@@ -222,46 +205,34 @@One final note about acs_objects. By setting - an object's
security_inherit_pcolumn to 'f', you can stop permissions + an object's security_inherit_p column to 'f', you can stop permissions from cascading down the context tree. In the following example, Joe does not have the read permissions on C and F. -
-
-A
-object_id=10
+
+A
+object_id=10
readable�by�Joe
- ������-
-B
-object_id=20
+ ������
+B
+object_id=20
readable�by�Joe
-��������������-
-C
-object_id=30
+��������������
+C
+object_id=30
security_inherit_p�=�'f'
not�readable�by�Joe
- ������- -
-D
-object_id=40
- ������- -
-E
-object_id=50
- ������-
-F
-object_id=60
+ ������
+D
+object_id=40
+ ������
+E
+object_id=50
+ ������
+F
+object_id=60
security_inherit_p�=�'f'
not�readable�by�Joe
- ������
Privileges are also organized hierarchically. In addition to the five main system privileges defined in the ACS Kernel data model, application developers may define their own. Note, @@ -276,14 +247,14 @@ admin privilege to which the first four privileges are tied. Privileges are structured as follows.
| admin | |||
| create | delete | read | write |
- Note that admin privileges are
+ Note that admin privileges are
greater than read, write, create and delete privileges combined.
Issuing someone read, write, create and delete privileges will
not result in the person getting
- admin privileges.
The parent-child relationship between privileges is represented in
- the acs_privilege_hierarchy table:
+ admin privileges.
The parent-child relationship between privileges is represented in + the acs_privilege_hierarchy table:
- create table acs_privilege_hierarchy ( + create table acs_privilege_hierarchy ( privilege not null constraint acs_priv_hier_priv_fk references acs_privileges (privilege), @@ -297,7 +268,7 @@ As in the case of the context hierarchy, it is convenient to have a flattened representation of this hierarchal structure. This is accomplished by defining the following view.- create or replace view acs_privilege_descendant_map + create or replace view acs_privilege_descendant_map as select p1.privilege, @@ -322,59 +293,51 @@ reasonably small, there is no pressing need to cache the flattened ansector-descendant view of the privilege hierarchy in a specially maintained table like it is done in the case of the context hierarchy. -
Now for the third hierarchy playing a promiment role in the permission system. The party data model is set up as follows. -
- create table parties ( ++ create table parties ( party_id not null constraint parties_party_id_fk references acs_objects (object_id) - constraint parties_party_id_pk primary key, + constraint parties_pk primary key, email varchar2(100) constraint parties_email_un unique, url varchar2(200) );- create table persons ( + create table persons ( person_id not null constraint persons_person_id_fk references parties (party_id) - constraint persons_person_id_pk primary key, + constraint persons_pk primary key, first_names varchar2(100) not null, last_name varchar2(100) not null );- create table users ( + create table users ( user_id not null constraint users_user_id_fk references persons (person_id) - constraint users_user_id_pk primary key, + constraint users_pk primary key, password char(40), -- other attributes );- create table groups ( + create table groups ( group_id not null constraint groups_group_id_fk references parties (party_id) - constraint groups_group_id_pk primary key, + constraint groups_pk primary key, group_name varchar2(100) not null );- Recall that the
grantee_idcolumn of the + Recall that the grantee_id column of the acs_permissions table references -parties.party_id. + parties.party_id. This means that you can grant a privilege on an object to a party, person, user, or group. Groups represent aggregations of parties. The most common scenario that you are likely to encounter is a group that is a collection of users, although you could also @@ -385,9 +348,9 @@ a group named Pranksters, you can assign membership to Pete, Poly, and Penelope. The fact that these users are members of the Pranksters group will be recorded in the -membership_relsandacs_relstables: + membership_rels and acs_rels tables:- create table acs_rels ( + create table acs_rels ( rel_id not null constraint acs_rels_rel_id_fk references acs_objects (object_id) @@ -405,7 +368,7 @@ unique (rel_type, object_id_one, object_id_two) );- create table membership_rels ( + create table membership_rels ( rel_id constraint membership_rel_rel_id_fk references acs_rels (rel_id) constraint membership_rel_rel_id_pk primary key, @@ -417,13 +380,7 @@The acs_rels table entries would look like so: -
- rel_type-- object_one-- object_two-+
rel_type object_one object_two membership_rel Pranksters @@ -441,34 +398,28 @@ Pranksters Penelope - Read
acs_rels: right-side is a +Read acs_rels: right-side is a subset of left-side, ie -
object2is a part of -object1. + object2 is a part of + object1.Another way of building up groups is by adding subgroups. Suppose we define Merry Pranksters and Sad Pranksters as subgroups of Pranksters. We say that the Pranksters group - is composed of + is composed of groups Merry Pranksters and Sad Pranksters. This information is stored in the acs_rels - and
composition_relstables. + and composition_rels tables.-create table composition_rels ( +create table composition_rels ( rel_id - constraint composition_rel_rel_id_fk references acs_rels (rel_id) - constraint composition_rel_rel_id_pk primary key + constraint composition_rels_rel_id_fk references acs_rels (rel_id) + constraint composition_rels_rel_id_pk primary key );The relevant entries in the acs_rels look like so. -
- rel_type-- object_one-- object_two-+
rel_type object_one object_two composition_rel Pranksters @@ -498,7 +449,7 @@ reducing the performance hit incurred by hierarchical queries is to cache query results in a table maintained by triggers. The OpenACS data model defines two such tables: - create table group_component_index ( + create table group_component_index ( group_id not null constraint group_comp_index_group_id_fk references groups (group_id), @@ -517,7 +468,7 @@ primary key (group_id, component_id, rel_id) ) organization index;- create table group_member_index ( + create table group_member_index ( group_id not null constraint group_member_index_grp_id_fk references groups (group_id), @@ -534,11 +485,11 @@ primary key (member_id, group_id, rel_id) ) organization index;- The
group_component_indextable stores a flattened representation of the + The group_component_index table stores a flattened representation of the group composition hierarchy that is maintained in sync with the acs_rels - andcomposition_relstables through triggers. -additional comments
- As far as the
group_member_indextable goes, I am not sure I understand its + and composition_rels tables through triggers. +additional comments
+ As far as the group_member_index table goes, I am not sure I understand its purpose. It maintains group-member relationships that are resolved with respect to group composition. Note that information stored in group_member_index can be trivially derived by joining @@ -569,7 +520,7 @@ mr.rel_id = r.rel_id and r.object_id_one = gci.component_id;
- A heuristic way to verify that
group_member_viewis essentially identical + A heuristic way to verify that group_member_view is essentially identical to group_member_index is to compute the symmetric difference between the two:@@ -597,16 +548,16 @@ membership relationship resolution can be computed trivially with no hierarchical queries involved. There is no need to keep the view in a denormalized table, unless doing so results in substantial performance gains. -- Security information is queried by calling the
acs_permission.permission_p++ Security information is queried by calling the acs_permission.permission_p function in OpenACS. This is accessible from Tcl via the -
permission::permission_pprocedure. + permission::permission_p procedure.create or replace package body acs_permission as -- some stuff removed for the sake of brevity - function permission_p ( + function permission_p ( object_id acs_objects.object_id%TYPE, party_id parties.party_id%TYPE, privilege acs_privileges.privilege%TYPE @@ -624,15 +575,15 @@ end; end acs_permission; -problem avoidance
+
problem avoidance
The function queries acs_object_party_privilege_map, which is a humongous view that joins three flattened hierarchies: the context tree, the privilege hierarchy, the party composition (and membership) hierarchy. It contains an extremely large number of rows. About the only kind of query you can run against it is the one - performed by the
acs_permission.permission_p+ performed by the acs_permission.permission_p function. Anything other than that would take forever to finish or would ultimately result in a query error.@@ -668,7 +619,7 @@ end; /
- The
acs_permission.revoke_permissionfunction merely runs a + The acs_permission.revoke_permission function merely runs a delete statement like so:delete from @@ -678,15 +629,9 @@ and grantee_id = revoke_permission.grantee_id and privilege = revoke_permission.privilege;- Note that in the above example,
acs_permissionshad only + Note that in the above example, acs_permissions had only one entry that needed to be deleted: -
- object_id-- grantee_id-- privilege-+
object_id grantee_id privilege default_context registered_users @@ -695,9 +640,9 @@ The above script would never get around to deleting this entry because it had to loop through a gazillion rows in the humongous -
acs_object_party_privilege_mapview. -+create or replace view acs_object_party_privilege_map as select ogpm.object_id, @@ -716,7 +661,7 @@ from acs_object_grantee_priv_map;-create or replace view acs_object_grantee_priv_map +create or replace view acs_object_grantee_priv_map as select a.object_id, @@ -728,7 +673,7 @@ where a.privilege = m.privilege;-create or replace view acs_permissions_all +create or replace view acs_permissions_all as select op.object_id, @@ -740,7 +685,7 @@ where op.ancestor_id = p.object_id;-create or replace view acs_object_paths +create or replace view acs_object_paths as select object_id, @@ -750,7 +695,7 @@ acs_object_context_index;-create or replace view group_member_map +create or replace view group_member_map as select group_id,