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Software Reuse

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Software systems design traditionally assume that components are ... ( Billing systems, payroll systems, registration systems) What does this mean in practice? ... – PowerPoint PPT presentation

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Title: Software Reuse


1
Software Reuse
  • This is the concept that all or part of a
    computer program can be re-used at a later time.
  • A technique which attempts to save time, energy
    and money by reducing the duplication of work.
  • Adapted from http//en.wikipedia.org/wiki/Software
    _reuse

2
Software Reuse
  • The design process in most engineering
    disciplines is based on component reuse.
  • Software systems design traditionally assume that
    components are implemented specifically for the
    system being developed.

3
Software Reuse
  • Examples
  • Software libraries
  • Subroutines, objects or classes
  • BUT! What about larger portions of code?

4
Software Reuse
  • Reusable components and frameworks are inherently
    abstract, making it hard to create quality
    components and hard manage their production.
  • The skills required to develop, deploy, and
    support reusable software have traditionally been
    a black art, locked in the heads of expert
    developers.
  • These technical impediments to reuse are
    compounded by common non-technical problems that
    add additional organizational, economical,
    administrative, political, and psychological
    difficulties.
  • Adapted from http//www.cs.wustl.edu/schmidt/reus
    e-lessons.html

5
Software Reuse
  • In principle, organizations recognize the value
    of systematic reuse and reward internal reuse
    efforts.
  • In practice, many factors conspire to make
    systematic software reuse hard.

6
Software Reuse Non Technical Issues
  • Organizational impediments -- Developing,
    deploying, and supporting systematically reusable
    software requires a deep understanding of what
    the application developer needs and business the
    requirements.
  • Economic impediments -- Supporting
    organization-wide reusable components requires an
    economic investment.
  • Administrative impediments Reusable components
    are hard to catalog, archive, and retrieve,
    especially across multiple business units within
    large organizations. Developers often find it
    hard to locate suitable reusable assets outside
    or even inside their immediate workgroups.

7
Software Reuse Non Technical Issues
  • Political impediments -- Groups that develop
    reusable software are often viewed with suspicion
    by other application developers.
  • Psychological impediments
  • Application developers may also perceive top
    down reuse efforts as an indication that
    management lacks confidence in their technical
    abilities.
  • The not invented here syndrome is ubiquitous in
    many organizations, particularly among highly
    talented programmers.

8
Software Reuse
  • Common reuse -- Components only
  • This is slowly changing
  • Why?

9
Software Reuse
  • Demand for lower software costs.
  • Reuse enhances improved reliability
  • Reused components are "proven."
  • Design and implementation faults are discovered
    and "eliminated."

10
Software Reuse
  • Reuse shouldn't focus just on code but on
    design....

11
Software Reuse
  • Code may contain specialized details that make
    reuse difficult.
  • Designs are by nature more abstract having wider
    application.

12
Reuse can occur at different levels
  • Application system reuse
  • Sub-system reuse
  • Module or object reuse
  • Function reuse

13
Application system reuse
  • The whole application may be reused
  • Key problem gt portability

14
Sub-system reuse
  • Major sub-system of an application may be reused.

15
Module or object reuse
  • Components of a system might be reused
  • Java object for a binary tree

16
Function reuse
  • Software component for a single function
    (method) might be reused
  • Ex mathematical function

17
Software Reuse
  • Application system reuse is widely practiced.
    (Billing systems, payroll systems, registration
    systems)
  • What does this mean in practice?

18
Software Reuse
  • Function reuse is also common.
  • Individual developer designed tools
  • Java API
  • Game components
  • How is this different from application system
    reuse?

19
WHY Reuse?
  • Reduce development costs
  • Increase system reliability
  • Reduce overall process risk
  • More effective of specialists
  • Organizational standards can be built-in.
  • Software development time reduced.

20
But...
  • To make effective use of reusable components we
    cannot first design a system and THEN search for
    reusable components.
  • The design process MUST be reuse driven.

21
Software Reuse
  • System requirements must be modified according to
    the availability of reusable components.

22
Reuse Problems
  • Difficult to quantify cost reduction
  • CASE tools do not really support reuse
  • Some software engineers prefer to rewrite
    components

23
Rewrite Components
  • WHY?
  • Poor techniques for classifying, cataloging and
    retrieving software components
  • Legal issues

24
Systematic reuse requires a properly cataloged
and documented database of reusable components.
  • WHY??

25
Intellectually, we assume that a reuse database
exists
  • In most places such databases are fiction!

26
Components that are created as part of an
applications development are NOT likely to be
immediately reusable.
  • WHY??

27
Software Reuse
  • Creating reusable components is difficult
  • To make a component truly general, ALL the
    operation classes that might be needed must be
    specified.

28
Software Reuse
  • Current reuse focuses on portability issues.

29
Reuse Problems
  • Special features of individual machines
  • Machine architecture
  • Operating system
  • Run-time system
  • Library problems

30
Machine architecture
  • The program makes assumptions about the
    underlying hardware -- these assumptions are
    rarely true for ALL machines

31
Operating system
  • Program call operating system facilities that are
    not available on ALL host machines

32
Run-time system
  • Program uses particular run-time system features
    which are not universal
  • (ex. dynamic checking)

33
Library problems
  • Not all libraries are available on all machines.
  • Not all libraries contain everything you might
    expect them to include.

34
Reuse Solutions???
  • Reduce the use of special features -- Create
    Standards
  • Programming language
  • Operating system
  • Networking
  • Window system

35
Reuse -- Legal Issues
36
Software Reuse
  • Do we need to Invent or Create a Super-
    Language?
  • Is Java that language or even that style of
    language?
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