Person Attribute Group Store (PAGS) Overview

PAGS Overview

The PAGS defines group memberships by logical expressions on attributes retrieved by PersonDirectory. (PersonDirectory initializes IPersons with attributes retrieved from one or more sources of directory information, including, for example LDAP.)

Capabilities of PAGS

PAGS computes entity memberships by testing the value of selected IPerson attributes. Like PersonDirectory, the PAGS retrieves information one user at a time. As a result, it can answer inquiries about what groups a particular IPerson or _group member_ belongs to, but it cannot answer inquiries about what entity members are contained by a given group.

Can do:

contains()
find()
findContainingGroups()

Can't do:

findEntitiesForGroup()

Although PAGS groups cannot answer their entity members, they are aware of their member groups.  So they can also do:

Can do

findMemberGroupKeys()
findMemberGroups()

This will usually suffice for authorization, so the PAGS can be thought of as an authorization-oriented group store. Since PersonDirectory supplies information about IPersons and not about ChannelDefinitions or other portal entities, a further limitation is that the PAGS can only contain memberships associating IPerson group members with IPerson groups.

The configuration lets you do 2 things: (i) declare IEntityGroups with key, name, description and member group keys, and (ii) declare the tests that determine if an IPerson is a member of a group. Since a group need not contain any member groups, the <members> element is optional. Since a group need not contain any member entities, the <selector-test> element is also optional.

Tests. Each of the tests to be applied to an IPerson is described in a <test> element, which consists of 3 required sub-elements, the name of the test class, the name of the attribute to be tested, and the value against which the attribute is to be tested by the tester class. In the example below, the test is true if the String value of the attribute "sn" equals "Jones".

<test>
    <attribute-name>sn</attribute-name>
    <tester-class>org.jasig.portal.groups.pags.testers.StringEqualsTester</tester-class>
    <test-value>Jones</test-value>
</test>

The PAGS currently ships with 8 tester classes, and you can easily create your own.  Each tester class must implement the IPersonTester interface, which consists of a single method:

 public interface IPersonTester {
    public boolean test(IPerson person);
}

The following tester classes (all in the package org.jasig.portal.groups.pags.testers) come with PAGS:

Test Groups. Individual tests are aggregated into test groups, and their results are AND-ed together, so all tests in a test group must return true for the test group to return true. A test group is described by a <test-group> element. If there is more than 1 <test-group> element, the results of the test groups are OR-ed together, so if any one test group returns true, the tests return true.  A true result means that the candidate IPerson is a member of the group. 

Multi-valued attributes. The testers that come with PAGS will OR the tests of successive values of a multi-valued attribute, so if any value satisfies the test, the test returns true.  You can override this behavior in a custom tester. 

Caching of group store information.  Because the groups structure defined in the PAGS is invarient, an instance of each group, including the keys of its containing groups, is cached by the store on start-up.  These cached instances are dealt out to satisfy all requests to the store for groups.  As a result, any change to the store configuration (via PAGSGroupStoreConfig.xml) requires restarting the group service, which generally means restarting the portal.  By contrast, memberships for an IPerson group member are cached for the life of the corresponding user's portal session.  As a result, if an IPerson's attributes change, these new attributes -- and any group memberships they imply -- will be visible on next log in. 

Recursive Testing.  If one PAGS group (the child group) belongs to another PAGS group (the parent group), then an IPerson member of the child group must also pass the test(s) required for membership in the parent group.  This is a more restrictive contract than the group system in general requires, where membership in a group only means that some relationship exists between a group and its members.  Here, when an entity group member belongs to a group, it means that the underlying entity has some specific attribute value(s).  The PAGS enforces this by testing the entity for membership in all its parent groups, which means you can nest the testing of entity members.  For example, assume a group named named "employees" requires status equal to "employed" and a group named "seniors" requires age GE 65.  If "seniors" is a member of "employees", then any IPerson member of "seniors" is required to have both age GE 65 and status equal to "employed".