Re: [I2nsf] Service Level Policies - Post 4: differentiating between context, conditions, and Constraints

[John Strassner <[e-mail]>]

Hi Linda,

The answer depends if I2NSF wants to pursue authorization policies and/or
deontic or alethic logic.

If any of the above three are true, then "Subject" must change.

If we step back for a moment and think about the definition of an ECA
policy rule (event-condition-action), then I remain unconvinced why this is
not sufficient for us at the moment. More specifically:

   1) Subject-Object-Action-Function does not have a facility for
representing Events, which start policy processing
   2) Subject, as currently defined, is just part of a condition
   3) Object, as currently defined, is also just part of a condition (more
specifically, object constraints do NOT apply to anything else)
   4) Function(al profile) needs more specificity, but appears to be able
to be covered by metadata (see below).

So, if we view a policy rule as a **container**, then the container
aggregates both metadata and content. Metadata can be prescriptive and/or
descriptive; content is the type of policy (or set of policies) contained
in the container.

This is the subject of my last 2 remaining posts, but in a nutshell, I do
not see a need for using Subject-Object-Action-Function, since this
introduces non-standard terminology, and the terms are unclear. If the
objective is **just** to categorize what type of processing can be done by
an NSF, **and if** it is desired to link I2NSF to policy, then I don't see
why we can't use a standard ECA policy, augmented with metadata, to do this.


regards,
John

On Fri, Jan 8, 2016 at 9:51 AM, Linda Dunbar <[e-mail]>
wrote:

> John,
>
>
>
> Thank you very much for clarifying the differences among
>
>
>
> The term “Object” in I2NSF was intended for describing all three “Context,
> Conditions and Constraints”.
>
> I agree it is not very straight forward definition.
>
>
>
> Do you Suggest I2NSF should have something like:
>
>
>
> Within the frame of “Subject - <xxx> - Action –Function”, <xxx> is the
> combination of “Context, Conditions and Constraints”.
>
>
>
> Should we call it “CCC”?  Or do you have a better term?
>
>
>
> Linda
>
>
>
> *From:* I2nsf [mailto:[e-mail]] *On Behalf Of *John
> Strassner
> *Sent:* Thursday, January 07, 2016 4:09 AM
> *To:* [e-mail]
> *Subject:* [I2nsf] Service Level Policies - Post 4: differentiating
> between context, conditions, and Constraints
>
>
>
> During IETF94, I expressed discomfort with the
> "Subject-Object-Action-Function" paradigm. This note defines and
> differentiates between the concepts of context, constraints, and conditions.
>
>
>
> 1.  Context
>
>
>
> There are many definitions of context. One of the most popular [1] is:
>
>
>
>    ‘‘Context is any information that can be used to characterize the
> situation
>       of an entity. An entity is a person, place, or object that is
> considered
>       relevant to the interaction between a user and an application,
> including
>       the user and application themselves’’.
>
>
>
> As stated in [2], the above definition has a number of problems. Instead,
> [2] proposes the following definition:
>
>
>
>    "The Context of an Entity is a collection of measured and/or inferred
>
>      knowledge that describe the state and the environment in which an
>      Entity exists or has existed."
>
>
>
> The above definition enables human and or machine inference to be used to
> more fully characterize the context of an Entity.
>
>
>
> 2.  Conditions
>
>
>
> An event-condition-action (ECA) policy rule consists of three Boolean
> clauses, and has the following conceptual behavior:
>
>
>
>    IF the event_clause evaluates to TRUE
>
>       IF the condition_clause evaluates to TRUE
>
>          THEN execute the actions in the action_clause
>
>       ENDIF
>
>    ENDIF
>
>
>
> Each of the above clauses may consist of one or more statements. For
> example, a condition clause could be:
>
>
>
>    if userLogin = Error AND numLoginTries > 3
>
>
>
> 3.  Constraints
>
>
>
> A constraint is a limitation or restriction. Constraints have been used in
> programming and in modeling for a long time. Constraint programming refers
> to the embedding of constraints in a language; for example, most Prolog
> languages include good support for constraint programming. OCL (the Object
> Constraint Language) is used to specify constraints in UML.
>
>
>
> 4. Putting Context, Conditions, and Constraints Together
>
>
>
> Given a condition, a constraint can be used to further restrict how to
> satisfy the condition. Then, if a context is specified, the condition and
> its constraint are bound to that context. In an ECA policy rule, the effect
> of this is typically to more fully specify the condition clause.
>
>
>
> Note, however, that constraints do not have to be used solely with
> Conditions. For example, a constraint can be used to specify when it is
> safe to transition to a new state. As another, more powerful, example, the
> concept of a software contract [3] uses constraints to extend the
> definition of Abstract Data Types to formally define the behavior of
> software components. Simplifying the theory, this says the following:
>
>
>
>   In order for a method to execute,
>       a set of pre-conditions must be satisfied before the method can
> execute
>       a set of post-conditions must be satisfied when the method is
> finished
>       a set of invariants must not change their value during the execution
>
> ·  The set of pre- and post-conditions, along with invariants, are all
> constraints.
>
> 5. Proposal
>
>
>
> Context, conditions, and constraints are separate concepts, but they fit
> together naturally.
>
>
>
> With respect to policies, if a policy is viewed as a (software) container,
> then context is applied to the container (and hence, to the components of
> the container).
>
>
>
> Constraints can be applied to terms in each of the event, condition, and
> action clauses of an ECA policy rule to restrict their behavior, data type,
> domain and range, and so forth. The most common examples are applying
> constraints to conditions or to govern the behavior of actions.
>
> ·  [1] Dey, A., "Providing Architectural Support for Building
> Context-Aware
>      Applications, Ph.D. Thesis, 2000
>
> [2] Strassner, J., et al., "The Use of Context-Aware Policies and
>      Ontologies to Facilitate Business-Aware Network Management",
>      Journal of Network and Systems Management (17), pg 255-284, 2009
>
> ·  [3] Meyer, B., "Object-Oriented Software Construction, 2nd edition,
>      Prentice-Hall, ISBN:  0-13-629155-4
>
>
>
>
> --
>
> regards,
>
> John
>



-- 
regards,
John