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?