Articulating Flexibility

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• Articulating Flexibility

Nature of Flexibility
Desire for Flexibility
Promise of Flexibility
Discussion Close
Nurture of Flexibility
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Key Questions

• Where is the demand for flexibility coming from?
• Is anyone willing to pay for flexibility? Should
  they?
• What are the various responses to the demand for
  flexibility
• Perennial claims by vendors and others - the
  silver bullet point
• Architectural patterns - separation of concerns
• How do we evaluate these responses?
• Which responses are appropriate for which demands?

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Myths of flexibility

• Flexibility is always a Good Thing.
• Flexibility is a linear characteristic - you can
  have more or less of it.
• Flexibility is expensive.
• Flexibility is free - if youre using the right
  instruments.

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Desire for Flexibility

• Specific Demand for Flexibility
• precise envelope of test conditions
• explicit demand for vague quality
• Ability to Respond to Demanding Change
• customers
• regulators
• management
• Escape from Legacy Constraints
• historic limitations of past solutions
• Protection from the Caprice of the Environment
• management interference
• enterprise improvidence
• Tolerance of Imperfect Requirements
• specification errors
• procurement errors

Where is the demand coming from?
Who wants flexibility - flexibility for whom?
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Promise of Flexibility

• Flexible solutions built from flexible components
• Flexible solutions built from disposable/interchan
  geable components
• Flexible solutions built upon flexible platforms

But how much is flexibility worth - and for whom?
And we provide superior flexibility
Who benefits from One Size Fits All?
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Patterns for Flexibility

• Vague Boundaries
• Loose Fit
• Double Boundaries
• Buffered Fit
• Differentiated Service
• Multiple Fit
• True Polymorphism
• Universal Fit

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Where is Flexibility Located?

• In the components?
• Self-description
• In the component kit?
• Replacement
• In the architecture?
• Layering
• In the policy layer?
• Recalibration
• In the development process?
• Rapid development
• Just-in-time maintenance

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Nature of Flexibility

• Contortionist View
• The ability to make a wide range of changes in
  response to the environment.
• The ability to accommodate oneself to the changes
  in the environment.

• Homeostatic View
• The ability to preserve or maintain something
  essential in the face of environmental change.
• The ability to keep working under changed
  circumstances.

• Measure Internal Changes
• How many options configurations?
• At design time?
• At installation time?
• At run time?
• After just-in-time maintenance?

• Measure External Changes
• How many opportunities and scenarios?
• Without manual adjustment.
• With manual adjustment

XXX is as flexible as concrete
One Size Fits All?
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Flexibility as Second-Order Requirement

• 1st-Order Requirements
• Specifies the relationship between the solution
  and the users.
• This is what the system should do.
• This is how the users may interact with the
  system.
• This is the quality of service that the users may
  expect.

• 2nd-Order Requirements
• Specifies the relationship between the solution
  and the requirements.
• Flexibility This is the extent to which the
  system accommodates new requirements.
• Security This is the extent to which the system
  can protect itself against new tricks.

• Acceptance Test
• How does the system deal with a range of test
  cases?
• How does the system deal with a range of test
  conditions?

• Acceptance Test
• How does the system management deal with various
  surprises and innovations?

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Principles of Flexibility

• Flexibility is implicit in the demand.
• Situations possess certain properties that demand
  flexibility in the solution.
• uncertainty / risk
• variety / tension
• change
• Flexibility may be contained in the solution.
• Solutions possess certain properties that may
  respond to the demand.
• requisite variety
• robustness
• adaptability
• contingency

• Engineers must match the flexibility implicit in
  the demand with the flexibility contained in the
  solution.
• scenario planning
• contingency planning
• Managers must reason intelligently about
  flexibility and change.
• business case
• return on investment
• business continuity and survival

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False Routesto flexibility

• Simplistic attempts to increase flexibility often
  result in a loss of flexibility.
• Anticipating Complexity
• Build a general-purpose solution that will
  satisfy all the future requirements you can think
  of, as well as the present requirements the users
  have asked for.
• Hesitation
• Flexibility is achieved not by keeping your
  options open, but by making decisions. Keeping
  your options open is a form of neurosis, and
  leads to paralysis. Bateson calls this a narrowly
  homeostatic system, rigidly indecisive. (It is a
  characteristic of schizophrenic families.)
• Exporting Uncertainty and Risk
• Dumping the responsibility and cost for future
  variation on subcontractors or other business
  partners - but this often increases the overall
  turbulence in the market, with negative
  consequences for all players.

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Shearing layers

• Complex artefacts tear themselves apart.
• The dynamics of the system will be dominated by
  the slow components.

Stuff
Space Plan
Services
Skin
Structure
Site
Source Stewart Brand, How Buildings Learn
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Managing the evolution of complex artefacts.
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SatisfiesRequirements
Caprice
System
Over/Under Determined
Self-Organizing
Environment
Closed
Turbulent
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Key Messages

• There is a widespread belief in the business or
  social value of flexibility.
• A truly flexible business would adapt easily to
  changing demands and conditions, and could
  accommodate social and cultural diversity and
  this in turn would depend (among other things) on
  flexible computer systems and platforms.
• We think we can recognize flexibility - and lack
  of flexibility.
• There are many solutions in the IT world that are
  promoted as flexible, or helping to deliver
  flexibility.
• There are also solutions (including legacy and
  COTS) that are widely criticized as inflexible.
• Most claims of flexibility are based on unfounded
  optimism and unverifiable wisdom.