Real Time Systems

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Real Time Systems

• Patterns
• AntiPatterns

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Review
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Outline

• Patterns
• Definitions
• Classic Design Patterns
• Examples
• AntiPatterns
• Definitions
• Examples

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What is a Pattern?

• Each pattern describes a problem which occurs
  over and over again in our environment, and then
  describes the core of the solution to that
  problem, in such a way that you can use this
  solution a million times over, without ever doing
  it the same way twice
• Christopher Alexander

Quite simply, it is just design reuse
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What is a Classic Design Pattern?

• A design pattern describes a commonly-recurring
  structure of communicating components that solve
  a general design problem in a particular
  context.
• Gamma et al

Sounds very OO-like, in fact it sounds a lot
like ROOM Selic et al !
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Why Use Patterns?

• advantages of design patterns are reusability and
  modularity, which are precisely the goals of
  object-oriented software design.
• because design patterns capture expert knowledge,
  the solutions it provides are tried and true.
  Therefore, they not only make it less
  time-consuming to design a large system, it also
  improves design quality.

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Why Use Patterns?

• design patterns provide a common vocabulary for
  designers to communicate by expressing software
  design at higher level of abstraction than that
  of a design notation or programming language.
• being able to recognise design patterns helps one
  to understand existing systems.

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Examples of Design Patterns

• Composite Pattern Gamma et al

What real software systems might contain this
pattern?
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Examples of Design Patterns Recognize this one?
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Examples of Design Patterns Recognize this one?
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AntiPatterns

• An antipattern describes an approach to solving
  a common problem, an approach that in time proves
  to be wrong or highly ineffective. Ambler
• An AntiPattern is a literary form that describes
  a commonly occurring solution to a problem that
  generates decidedly negative consequences. The
  AntiPattern may be the result of not knowing
  any better, not having sufficient knowledge or
  experience Brown et al

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Examples of AntiPatterns

• The Blob (Winnebago, the God Class)
• Functional Decomposition (No OO)
• Spaghetti Code
• Boat Anchor
• Golden Hammer

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Exercise

• What patterns and antipatterns might we find in
  our RoseRT labs?

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References

• Selic, B., Gullekson, Ward, Real-Time
  Object-Oriented Modeling, Wiley, 1994.
• Ambler, S., The Object Primer, Cambridge Univ.
  Press, 2001, Chapter 7.
• Gamma, E., et al, Design Patterns, Addison
  Wesley, 1994.
• Brown, Malveau, McCormick, Mowbray, AntiPatterns
  Refactoring Software, Archictectures, and
  Projects in Crisis, Wiley Sons, 1998.
• Douglass, B.P., Real-Time Design Patterns Robust
  Scalable Architecture for Real-Time Systems,
  Addison-Wesley, 2003.

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Questions