Use of Concept of Transparency in the design of hierarchically structured systems

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Use of Concept of Transparency in the design of
hierarchically structured systems

• D.L. Parnas and D.P. Siewiorek

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Introduction

• Concept of Design
• Top-Down or Outside in Approach
• Difficulties Faced in this approach.

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Concepts

• What Does Transparency mean.
• Concept of Loss of Transparency.
• What Book Talks about(Example On Board.)

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Example From Work

• This example illustrates the loss of Transparency
  In a system called Client -Setup.
• Desirable loss as you will see.
• This system has a layer called Persister, which
  present a uniform view of the Database. All other
  layers use this layer, the Persister to access
  the database.

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Example contd.

• Now in Raw format you could call any sequence of
  this Persister APIs and there are lot of
  combinations you can try, but all are not allowed
  set of actions.
• There is an introduction of Rules Layer, this
  layer controls the sequence of calls you can
  make.
• Thus something that is possible with the
  Persister layer directly, is lost when this Rules
  Layer is added.

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Example Contd

• Figure

You can make any Combination of calls
Forms as a Layer Controlling the Sequence Of API
Calls
Rules
Persister
Database
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Example No loss of transparency

• A chemical mix plant mixes two chemicals c1,c2 to
  produce the chemical c3. The chemical c3 produced
  depends on the temperature of the mix. The agent
  creating the mix selects arbitrary quantities of
  c1 and c2 and arbitrary furnace temperature.
• The interface provides 2 controls for the
  selection of chemicals c1,c2 and another control
  for temperature. These 3 controls on the virtual
  machine combine to produce all states possible
  previously

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Suggestive Transparency

• Weaker form of transparency.
• User is able to provide feedback, but does not
  have actual control.
• Example Consider the problem for search space
  exploitation versus exploration. The e-greedy
  method exploits most of the time and explores
  with probability of e. The user is able to
  provide feedback to the system for exploration
  based on the value e.

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Misleading Transparency

• The Abstract layer misleads you to believe that
  everything is fine.
• Although when this layer is using the lower layer
  it is a very inefficient approach.

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Misleading Transparency

• Consider Insertion Sort in the base Layer, order
  of complexity N2
• There are algorithm which provide lesser
  complexity for the same operation (viz nlogn,
  Merge Sort).
• Virtual Layer hides this additional complexity
  from user.

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Conclusion

• That when Designing systems we should use both
  Bottom-up and Outside-in approach in conjunction.
• This should be done judiciously so as to make
  sure that what we have as base layers can be used
  to bring the over-all architecture to life.
• We can have all the mortar in the world but if
  steel is not there, building a high rise building
  out of this basic building block would be
  difficult, at the same time if we did not knew
  what kind of structure we were making we would
  not reach the end intended building.