Subject: draft on PCIM extensions submitted

From: Marcus Brunner <[email-masked]>
Date: Fri, 17 Nov 2000 09:53:32 +0100

We have just submitted a draft titled "Policy Framework Core Info Model
Extensions".
It basically contains a list of open issues together with some
preliminary proposals for solutions. 

Marcus

-- 

Dr. Marcus Brunner
C&C Research Laboratories
NEC Europe Ltd.

E-Mail: [email-masked]
WWW:    http://www.ccrle.nec.de/
personal home page: http://www.tik.ee.ethz.ch/~brunner

Adenauerplatz 6
D-69115 Heidelberg
Germany

Phone: +49 (0)6221/ 9051129
Fax:   +49 (0)6221/ 9051155

INTERNET-DRAFT                                         M. Brunner
<draft-brunner-policy-core-ext-00.txt>                 J. Quittek
Expires in six months                                  NEC Corporation

                                                       November 17, 2000

              Policy Framework Core Info Model Extensions
                 <draft-brunner-policy-core-ext-00.txt>

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   http://www.ietf.org/ietf/1id-abstracts.txt

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Abstract

   This memo should help starting the discussion on extensions of the
   Policy Framework Core Information Model (PCIM).  It does not replace
   nor change concepts used in PCIM, but tries to add concepts, which
   could help different application areas to define policies more easily
   by reusing some of the concepts proposed in this draft.  The draft
   basically tries to generalize concepts introduced by other drafts
   such as the Policy Framework QoS Information Model [PQIM].  The focus
   lies in means for specifying general conditions and actions.
   Additionally, group ordering, events, and variables are introduced.

1. Introduction

   PCIM as proposed today is a well defined as a high-level information
   model for policies. However, many concepts are useful for the simple
   case, whereas more complicated policies poses problems using the

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   classes available.  The other problem lies in a set of application
   areas using the basic model and adapt and enhance it to area specific
   needs.  It turns out that many concepts are developed again and
   again, e.g., filters, variables, simple conditions etc.

   The goal of this draft is to extend PCIM with general constructs,
   which may be used in other areas.  Basically, they center around
   generic definition of conditions and actions with the knowlege of the
   structure of the modeling language. They are heavily influenced by
   constructs used in [PQIM], [PMPLS], and [PIPSEC].

   The draft in its current state is far from being complete.  e.g., the
   definition of class do not contain any formal property definition
   yet.  However, the proposed concepts and the list of open issues
   should help discussing useful extensions to the core information
   model.

   Other authors are very welcome to contribute to make the policy
   framework core information model useful in various areas.

2. PolicyGroup Ordering

   In PCIM, the policyRule has a property Priority, which allows a
   manager to give a rule priority over others.  However, it is not
   specified what the scope of the priority is, in the system or in the
   group.

   We propose a class OrderedPolicyGroup, which has a property priority
   as well. This allows for prioritizing groups over other groups.
   Furthermore, groups within the OrderPolicyGroup are ordered via the
   rule's or group's priority property.  Additionally, the scope of the
   priority is only within that group, not globally as it could be read
   in PCIM.  Groups in OrderPolicyGroups not being of type
   OrderPolicyGroup or a derivative of it, have the least priority.

   Note, that the functionality could be placed in the aggregation
   PolicyGroupinPolicyGroup as well. (What is preferred?)

     NAME          OrderedPolicyGroup
     DERIVED FROM  PolicyGroup (defined in [PCIM])
     ABSTRACT      False
     PROPERTIES    Priority [int]

3. Conditions

3.1. BasicPolicyCondition

   This class refines the basic structure of the policyCondition class

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   defined in [PCIM] by using the triplet <variable>, <operator> and
   <variable>.  The SimplePolicyCondition of PQIM is similar in
   structure, and a special case of this one, where the right variable
   has a constant value.

   The operator is relational and the binding is given by the types of
   both sides. Whether the operator is statically of dynamically bound
   (variable type or value type) is for further study.

   If one of the variables evaluate to undefined, the condition
   evaluates to false.

   What kind of RelOperators do we want?

   For example, the RelOperator property values may be
     - equal, notequal, lessthan, greaterthan, lessthanequal,
       greaterthanequal, for totally ordered values
     - startswith, endswith, equals, contains, for strings
     - contains, in, equals, includes, intersects, for sets

     NAME          BasicPolicyCondition
     DERIVED FROM  PolicyCondition (defined in [PCIM])
     ABSTRACT      False
     PROPERTIES    firstVariable [ref PolicyVariable],
                   RelOperator [String],
                   secondVariable [ref PolicyVariable]

3.2. Class PolicyObjectTypeSelector

   Basically, PCIM  uses the policyRole property in the PolicyRule class
   in order to select a set of objects the rule should apply to.  The
   selection may be refined by conditions.

   This kind of condition is special in the sense, that it compares the
   set of objects available in the context (basically specified by the
   role) whether they are of the type specified in this condition. So
   the rule containing this selector in the condition list operates only
   on objects of the specific type. This is very convenient, because it
   allows a policy designer to specify the actions with the knowledge,
   that only objects of a specific type will pass the condition.

     NAME          PolicyObjectTypeSelector
     DERIVED FROM  policyCondition (defined in [PCIM])
     ABSTRACT      False
     PROPERTIES    SelectorClassName

3.3. Class PolicyAssociatedObjectSelector

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   The PolicyAssociatedObjectSelector provides means to select objects
   only if they are associated with objects of a certain type and the
   AssocObjectPolicyCondition evaluates to true.

   Note that the class has a association to PolicyConditions
   (PolicyConditionInAssocObjectSelector). With that it is possible to
   specify again a PolicyAssociationObjectSelector as the condition.
   This allows to recursivly hop throught associated object.

   Furthermore, note that the condition within this selector has a
   different context, compared to the condition itself.  Conceptually,
   the PolicyAssociatedObjectSelector takes a set of objects and checks
   for all of them, whether they are in an association of type
   AssociationClassName where the object in this association is of type
   AssocObjectClassName and the policy condition evaluates to true.

     NAME          PolicyAssociatedObjectSelector
     DERIVED FROM  policyCondition (defined in [PCIM])
     ABSTRACT      False
     PROPERTIES    AssociationClassName,           AssocObjectClassName,

3.4. Association PolicyConditionInAssocObjectSelector

   This association ties together the PolicyAssociatedObjectSelector
   with a PolicyCondition.

     NAME          PolicyConditionInAssocObjectSelector
     ABSTRACT      False
     PROPERTIES    selector [ref PolicyObjectTypeSelector[0..1]],
                   condition [ref PolicyCondition[0..1]]

4. Variables

   Variables may be global or local. We propose to use only local
   variables, which means a variable is always used in the context of an
   object.

4.1. Class PolicyAttributeVariable

   The PolicyAttributeVariable has an attribute name and a class name as
   properties. The class name specifies in what scope the attribute name
   is valid.  The class name is only used in cases, where attribute
   names are not globally unique.

   Conceptually, if the variable is used in a condition, it evaluates to
   the value of the attribute named by AttributeName.  Note, that this
   variable may be undefined. This means the basic condition it is
   contained in evaluates to false.

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     NAME          PolicyAttributeVariable
     DERIVED FROM  Policy (defined in [PCIM])
     ABSTRACT      False
     PROPERTIES    AttrClassName,
                   AttributeName

5. Actions

5.1. Class PolicyAttributeSetAction

   The AttributeSetAction is used to set or change a value of an
   attribute. The action has again a class name and an attribute name as
   property. The class name specifies what type of objects to set, and
   the attribute name specifies what attribute to change.  Note again,
   in case of globally unique attribute names, the class name is not
   used in the action.

   The semantic behind the AttributeSetAction is, that setting the
   attribute of an object results in the configuration of the real
   object, represented by that object.

   If the attribute is not compatible with the type of the value, the
   action is not performed.

     NAME          PolicyAttributeSetAction
     DERIVED FROM  PolicyAction (defined in [PCIM])
     ABSTRACT      False
     PROPERTIES    AttrSetClassName,
                   AttributeSetName,
                   value

6. Events

6.1. PolicyEvent

   An event is a mean for triggering a rule to be evaluated. The source
   of the event may be in- or outside of the policy engine.  Therefore,
   an event has in its basic version no source identification
   associated. However, classes derived from the base class may add the
   source, if needed.  The PolicyEvent has a time and date when it
   happened. It has a name. The event name is used to differ the events.
   It could be usefule to add a context string, which make different
   policy models more independet and less error prone, because of global
   name spaces.

   The semantic behind the event is open, but see the next section for
   conditions on events.  However, typically the name will also define
   the semantic of the event.

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     NAME          PolicyEvent
     DERIVED FROM  Policy (defined in [PCIM])
     ABSTRACT      False
     PROPERTIES    event_time,
                   event_date,
                   event_name

6.2. PolicyEventCondition

   The event condition evaluates to true if an event happened with the
   name specified in cond_event_name.  In general, there is no time
   constrain defined, until when the rule containing the event condition
   needs to be evaluated.  But depending on the execution environment of
   the policy rules, this may immediately trigger the evaluation of the
   policy rule containing the event condition.

   After evaluating all rules in the system, containing the event
   condition in its condition tree, the event does not exist anymore,
   and the condition is evaluating to false for all further evaluations
   until the event is created once more.

   Note that, with this definition of the semantic, we do not run into
   problems of nested conditions and rules, which contain associations
   to the same event condition. However, more advanced semantics are
   possible, but may produce difficult to implement semantic.

     NAME          PolicyEventCondition
     DERIVED FROM  PolicyCondition (defined in [PCIM])
     ABSTRACT      False
     PROPERTIES    cond_event_name

6.3. PolicyEventCreateAction

   The PolicyEventCreateAction creates an event with a certain name.
   This may be useful in cases, where you have multi-level policy
   systems running in the same execution environment.

     NAME          PolicyEventCreateAction
     DERIVED FROM  PolicyAction (defined in [PCIM])
     ABSTRACT      False
     PROPERTIES    create_event_name

7. Security Considerations

   The security considerations for this document are the same as those
   of the [PCIM] and are not further addressed in this version of the
   draft.

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8. Open Issues

8.1. Multi-Object Selectors

   There are many cases where you want to select two or more objects, in
   order to associate the two objects, or all objects in a set to each
   other.

8.2. Creation of Objects

   It could be very beneficial for policies to create objects just with
   the type information, and set the attributes afterwards.  However,
   what is the semantic of the creation of an object?

8.3. Creation of Associations

   Section 8.1, already mention the problem of multi-object selection.
   One goal could be the creation of a new association, between these
   objects.  This action would not be difficult to specify, but it is
   not useful without the multi-object selection.

8.4. Modification of Associations

   Until now, we have no means other than area specific actions, which
   allow a policy designer to implement the modification of an
   association, or its properties.

8.5. Expressions

   How can we set or change attributes and parameters of action by an
   expression (e.g., set bandwidth to 50% of the existing one)

8.6. IP specific filters

   Filters are used many times, why not specifing it in the PCIM
   extension.

9. References

   [PCIM]  B. Moore, E. Ellesson, J. Strassner, "Policy Core Information
           Model -- Version 1 Specification", Internet Draft,
           <draft-ietf-policy-core-info-model-06.txt>, May, 2000

   [PQIM]  Y. Snir, Y. Ramberg, J. Strassner, R. Cohen, "Policy
           Framework QoS Information Model", Internet draft,
           <draft-ietf-policy-qos-info-model-01.txt>, April 2000

   [PMPLS] K. Isoyama, M. Brunner, M. Yoshida, J. Quittek, R. Chadha,

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           A. Poylisher, G. Mykoniatis, A. Kind,F. Reichmeyer,
           "Policy Framework MPLS Information Model for QoS and TE"
           <draft-chadha-policy-mpls-te-01.txt>, December 2000.

   [PIPSEC] J. Jason, "IPsec Configuration Policy Model", Internet draft
           <draft-ietf-ipsp-config-policy-model-01.txt>, July 2000.

10. Authors' Addresses

   Marcus Brunner, Juergen Quittek
      NEC Europe Ltd.
      C&C Research Laboratories
      Adenauerplatz 6
      D-69115 Heidelberg, Germany
      Phone: +49 (0)6221 905110
      Fax:   +49 (0)6221 9051155
      Email: [brunner|quittek]@ccrle.nec.de

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