The Viable System Model

1
The Viable System Model CyberneticsRealizing
Self-Adaptive Software
School of Computing Mathematical Sciences

• Andy Laws

2
Presentation Overview

• Review the context and motivations for this work.
• Summarize some related work in this area.
• Outline the cybernetic foundations of our
  approach.
• See where this has taken us so far.
• Speculate on where these findings may take us in
  the future.

3
The Context
4
Software Engineering Considerations

• The aim of Software Engineering has been
  described as
• ...the systematic, principled, design and
  deployment of applications that fulfil softwares
  original promise - applications that retain their
  full malleability throughout their lifetime and
  that are as easy to modify in the field as they
  are on the drawing board. (Laddaga,1997)
• In the thirty years since its establishment as a
  discipline many techniques have been introduced
  in pursuit of this goal, e.g.
• structured programming - high-level languages- OO
  - process maturity etc. (Lehman, ) All require
  the software designer to predict every software
  circumstance and code to be provided to deal with
  the situation.
• While significant improvements and highly
  successful have undoubtedly resulted, these
  efforts have failed to deliver on-going
  malleability and most software systems exhibit a
  growing fragility caused by continual adaptation
  to meet changing requirements.
• There is growing evidence to suggest that it is
  time to reconsider the engineering and
  maintenance of software systems in a manner
  similar to physical products and that a more
  organic view of software should be adopted.

5
Coupled with this..

• Over the last two decades, the development of raw
  computing power coupled with the proliferation of
  computing devices has grown exponentially.
• The production of evermore complex, ambitious and
  connected systems distributed systems
  underpinned by internet developments
• Such complexity strains the ability to adapt and
  maintain such systems manually in a timely manner
  yet they are required to be consistently
  available, highly-resilient, highly dependable
  etc.
• Consequently, much recent attention has focused
  on devolving some of the responsibility for
  adaptive and evolutionary activities to the
  software itself.

6
Some Related Work
7
IBMs Autonomic Computing Approach

• Inspired by the autonomic function of the human
  central nervous system. Such autonomic control
  regulates temperature, breathing, heart-rate etc.
  at a sun-conscious level.
• Ideally, autonomic software systems will take
  care of the mundane elements of systems
  management themselves

8
Eight Characteristics of Autonomic Systems

• Self-knowledge - Detailed knowledge of
  constituent components, current status etc.
• Self-configuration/re-configuration - Adjustments
  to a changing environment
• Self-optimizing - Monitor constituent parts and
  optimize accordingly
• Self-healing - The ability to recover from
  malfunction
• Self-protecting - Detect, identify and protect
  itself from attack
• Environmentally aware know its environment, the
  context surrounding its activity and act
  accordingly
• Co-operative Interact with other systems in a
  heterogeneous world open standards
• Anticipatory anticipate and transparently
  implement the resources required to meet user
  goals

How these should be effectively structured is
still open to question.
9
A Cybernetic Approach
10
The Viable System Model

• Beers VSM implements a control communication
  structure via hierarchies of homeostats (feedback
  loops)
• 6 major systems ensure viability of the system
• Implementation S1
• Monitoring S2
• Audit S3
• Control S3
• Intelligence S4
• Policy S5
• Offers an extensible, recursive, model-based
  architecture, devolving autonomy to sub-systems

Autonomic Systems
Anticipatory Self-awareness Deliberative
11
Recursion in the Model

• Each System One is expected to develop as a VSM
  in its own right
• Consequently, the model is re-produced in its
  entirety at each level
• So this model contains further VSMs and is
  itself contained in a higher level VSM

12
Where this begins to get really interesting

• The recursive nature of the underlying model
  suggests that each System One should develop as a
  Viable System Model in its own right.
• If the recursion is pursued below the level of
  the human software team then we arrive at the
  level of the software system.
• This strongly implies that the software system
  should assume the same overall management
  structure as the human software process
• Consequently, we appear to have a theoretically
  supported management architecture for
  self-managing autonomic software

13
Bratman et als IRMA Architecture

• Bratman et als Intelligent Resource-Bounded
  Machine Architecture (IRMA), a classic BDI agent
  model
• It is noticeable that many of the elements
  contained in the model correlate directly to
  elements of the VSM
• So
• Planning Means-Ends Reasoning S3
• Opportunity Analyser Filtering S4
• Beliefs about the world S5
• Desires and Deliberative Process S5
• Intentions - S5 Policy passed to S3 for enactment
• It is also apparent that some elements are
  missing for Viability

14
J-Reference Model
15
A Viable Intelligent Agent Architecture

• Using Bratman et als IRMA approach and using the
  VSM as a reference model, we designed a Viable
  Intelligent Agent Architecture realizable using a
  multi-agent approach.
• The design specifies, in some detail, the higher,
  deliberative processes of adaptation.
• In some respects, the ready-mapping of existing
  IRMA components and the inclusion of viability
  components demonstrates the applicability of the
  VSM-based approach.

16
Perhaps more excitingly A Practical
ApplicationIn-Vehicle Telematics System (IVTS)

• IVTS cover a broad range of computer-based
  systems, these may include or combine
• Engine Management Systems
• Drivers Information Systems
• Vehicle Navigation Tracking Systems
• Collision Avoidance Systems
• Vehicle Security Systems
• Using Jini Java RMI allows distributed
  applications to be developed as a series of
  clients that interact with application services
  via a look-up service.
• The service-oriented abstraction considers a
  service as a logical concept that can be
  discovered dynamically by a client and used
  according to a contract of use

17
Monitoring Instrumentation Considerations

• In order to debug, monitor and manage Jini
  applications, a dynamic instrumentation system,
  based again on Jini technology has been developed
• Uses
• Monitor service - connects with an application or
  lookup service and observes dynamic parameters
• Logger utility - invoked by a monitor to record
  data
• Analyzer utility - invoked by a monitor to
  compute complex parameters
• A Management Service creates and controls the
  monitor service

• The instrumentation system is implemented by
  combining Jinis
• code mobility capabilities
• Javas dynamic proxies
• Jinis event models
• To apply instrumentation
• the management service requests the application
  service to set an instrumented parameter
• The Look-up service monitor detects a change of
  state and notifies client
• Management service wraps service in monitor
  service and sends proxy to client

18
Some Implications and Final Comments

• The complete realization of a self-adaptive
  autonomic software system using the conceptual
  guidance of classical cybernetics and the VSM
  still has some way to go. Indeed, it isnt yet
  clear that full realization is possible and there
  are still many problems outstanding.
• Nevertheless, the approach offers a recursive
  generalized architecture from human software team
  to self-managing software systems
• However, the inclusion of the anticipatory and
  deliberative (Systems 4 and 5) systems appear to
  offer a step forward from purely autonomic
  systems. Of course, this brings its own problems
  environmental modelling ?
• Nevertheless, using off-the-shelf technology that
  does not necessarily reflect this viewpoint
  exactly has allowed us to make significant
  progress and indicates that this approach may
  supply a ready-made theoretical underpinning for
  such software systems.

19
Speculations on further applications

• Without wishing to impinge on the following
  speakers domain
• The Grid
• Perhaps applicable as an architecture for
  sustainable, viable virtual grid-like systems?
• E-Science
• A similar requirement for viable, adaptive
  structures?

20
Thanks Any Questions?