Component Based Software Engineering

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Component Based Software Engineering

• Alex Liberton
• CSC340
• Dr Pulimood

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Objectives

• To clearly provide a definition for Component
  Based Software Engineering.
• To define a component
• Advantages and disadvantages of using CBSE
• Composition of two components
• My conclusion.

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Intro. To CBSE

• Component-based software engineering (CBSE) is an
  approach to software development that relies on
  software reuse.
• CBSE emerged from the failure of object-oriented
  development to support effective reuse. Single
  object classes are too detailed and specific.

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Components

• Components are more abstract than objects and
  classes. Thus, they can be considered to be
  stand-alone service providers.
• A short definition of a component
• A software component is a unit of composition
  with contractually specified interfaces and
  explicit context dependencies only. A software
  component can be deployed independently and is
  subject to composition by third-parties.
• Clemens Szyperski

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Components
Standardized - Follows a standard component
model Independent Usable without
adapters Composable External interactions use
public interface Deployable - Stand-alone
entity Documented Full documentation
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Issues and Challenges

• Components selection may lead to challenges.
• Trust
• Untrustworthy suppliers may supply components
  that do not perform as expect. (can lead to
  security breach or program failure)
• Certification
• There is no component certification group.
• Documentation
• Tests cannot be fully performed on a
  non-documented component
• Trade-offs
• Requirements set for the system may change with
  the functionality that components offer.

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Composition

• To use components together as one, composition
  must take place. (3 types)
• Sequential Composition
• Each component must have a working interface to
  glue together.
• Hierarchical Composition
• The calling of one component by another. The
  interface of a component must require the
  interface of the other.
• Additive Composition
• The combination of two or more component
  interfaces to create a new super-component

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The CBSE process
From a presentation by Ian Sommerville
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CBSE, Dangerous?

• When used correctly, component based engineering
  provides the reusability and ease of using
  components
• When used incorrectly, many things can go wrong
• Many different components may provide different
  functionalities, except meet the same
  requirements.
• If a program has no need for one of these extra
  functionalities problems may arise.
• An adapter must be used to provide for all
  functionalities in the component.

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Ariane 5

• In 1996, the first test flight of the Ariane 5
  launcher failed 37 seconds after lift-off.
• The failure was caused by a reused component that
  provided extra functionality.
• The component was previously developed for the
  Inertial Navigation System.
• Assumptions made for that system component did
  not hold for the Ariane 5.
• The functionality that failed was not even needed
  or used by the Ariane 5 launcher.

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Conclusions

• Using components successfully depends on a few
  variants.
• Trust
• Certification
• Validation
• If these three conditions are met, component
  based engineering is a new and useful tool in
  software development.