Some notes for Software Engineering -- Reuse

Reuse

While some software engineering projects require totally new approaches, designed from scratch, most projects have areas of similarity to work that has been done in the past. A great deal of time and effort can be saved by reusing software components from other projects.

Reuse is an old idea, starting with the creation of libraries of math and i/o routines to support common features of mathematical calculations.

To varying extents, reuse can be an important issue in analysis, design and implementation

• Analysis with reuse
  • Existing analyses, decompositions, standards and designs used as frameworks
  • Subproblems mapped to known problems
  • Vocabulary, classes and objects of existing systems used to understand new problems
  • Extensively used for user interfaces, device interfaces
  • Speeds system analysis
    • Major subsystems may be analyzed by filling in the blanks
    • Use of standards minimizes training
  • Tends to distort requirements
    • COTS (Commercial off the shelf) becomes a requirement, even when not appropriate
    • features in existing systems get included even if they are not needed
    • novel aspects of the problem get missed
• Design with reuse
  • Existing API, libraries, etc. provide a sound resource bases
  • New virtual resources can be built to reduce the gap between sub goals and resources
  • Helps to keep the design on a feasible track
  • Modes of reuse
    • System reuse -- reuse of a complete system to solve a problem
      • Accountings systems, office suites, graphics packages, ...
      • Databases
      • Networks, other infrastructure
      • Enterprise Resource Planning systems
    • Subsystem (component) reuse -- erector set approach
      • Procedural component reusue
        • procedure/subroutine/function libraries
        • driver plugin interfaces
      • Object-oriented component reusue
        • Class libraries
        • Abstract classes
          
        • Interfaces (protocols, plugins, drivers)
      • GUI-oriented component reusue -- JavaBeans
        http://java.sun.com/products/javabeans/docs/spec.html
        • standard plug-in components for GUI-based application builders
    • API and library reuse
  • Open source vs. closed source reuse
• Programming with reuse
  • Programming languages
  • Operating systems
  • Scripting languages
  • APIs, libraries, system calls
    • Macro libraries
    • Procedure/subroutine/function libraries
    • GUI APIs and templates
    • File systems
    • Database systems
    • ....
  • Utility programs
  • IDE's, GUI IDE's