Software Reuse

1
Software Reuse

• Take components of one product in order to
  facilitate the development of a different product
  with different functionality.
• Accidental reuse the developers of a new
  product realize that a component of a previously
  developed product can be reused in the new
  product.
• Deliberate reuse software components are
  constructed specifically with the potential
  future reuse in mind.

2
Advantage of Deliberate Reuse

• The process of reuse is easier since the
  components are well documented.
• The process of reuse is safer since the
  components are thoroughly tested.
• The maintenance is easier since there exists a
  uniformity of style in those reusable components.
• However, implementation of such components could
  be much more expensive.

3
Motivation

• Make new software product faster, cheaper, and
  better.
• Thousands of payroll programs and inventory
  programs.
• Why re-invent the wheels?

4
Impediments to Reuse

• Ego or NIH syndrome a routine cannot be any
  good unless I write it myself.
• Quality concerns cant be sure if the routine
  may introduce faults into the product.
• Retrieval problem e.g. 20,000 reusable
  components 125 of which are sort routines.
• Expensive in making the reusable components.
• Legal issues arisen with contract software.

5
Raytheon Missile System Division

• Basic actions across many products sort data,
  edit or manipulate data, combine data, explode
  data, update data, and report on data.
• Functional module reuse code fragment designed
  and coded for a specific purpose.
• Program logic structure reuse a framework that
  many section of it can be filled in by using
  functional modules.
• 40 60 of business application designs and
  modules could be standardized ad reused.

6
Toshiba Software Factory

• Modules
• Documentation of all kinds such as designs,
  specifications, contracts, and manuals.
• Reusable components are examined by a committee
  and properly organized in a database for future
  retrieval.
• Careful statistics are kept on the reuse rate of
  all components.

7
NASA Software

• Four categories of modules (45 in the first two
  categories)
• Reused without any changes
• Reused with slight revision (lt 25)
• Reused with major revision (gt25)
• Developed from scratch
• The reused modules are in general small, well
  documented, with simple interfaces and little I/O
  processing.

8
GTE Data Services

• Management commitment to the reuse of source code
  modules
• Cash incentives for each module accepted for
  possible reuse.
• Royalties when the module was actually reused.
• Increased management budget when project achieve
  high level of reuse.
• It was not necessary to build a huge inventory of
  reusable components.
• Emphasis was on large modules (10,000 LOC).

9
Hewlett-Packard

• A product of 20,000 noncomment lines of C was
  developed and later reused.
• Reduced fault rate
• Increased productivity
• Decreased delivery time
• 11 additional cost of development
• Integration costs of the new product were 19 of
  the cost of developing non-reusable product.

10
European Space Agency

• A disaster of software reuse a program used for
  the Ariane 4 rocket was reused for the Ariane 5
  rocket.
• Cause lack of exception handler for a
  out-of-range exception.
• Why mathematical analysis had provided the such
  exception was impossible for the Ariane 4 rocket.
• Software developed in one context must be
  retested when reused in another context.

11
Four Types of Design Reuse

• Library or toolkit
• Framework
• Design pattern
• Software architecture

12
Design Problems in OO

• Finding Appropriate Objects
• Determining Object Granularity
• Specifying Object Interfaces
• Specifying Object Implementations
• Putting Reuse Mechanisms to Work
• Relating Run-Time and Compile-Time Structures
• Designing for Change

13
Design Patterns

• Inspired by an architect Christopher Alexander
• Describe a problem which occurs over and over
  again in our environment, and then describe 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.
• Descriptions of communicating objects and classes
  that are customized to solve a general design
  problem in a particular context.

14
Essential Elements

• Pattern Name Describe a design problem, its
  solutions, and consequences in a word or two.
• Problem Describes when to apply the pattern.
• Solution Describes the elements that make up
  the design, their relationships,
  responsibilities, and collaborations.
• Consequences The results and trade-offs of
  applying the pattern.

15
Abstract Factory Patterns
16
An Example of Abstract Factory
17
Object Adapter Pattern
18
An Example of Adapter Pattern
19
Portability

• A product is portable if it is significantly
  easier to modify the product as a whole in order
  to run it on another compiler/hardware/OS
  configuration than to recode it from scratch.
• Hardware incompatibilities secondary storage
  drivers, different character codes
• OS incompatibilities syntactic difference in
  job control languages (JCL), virtual memory
• Numerical software incompatibilities
• Compiler incompatibilities

20
How to Achieve Portability

• Forbid programmers to use constructs that might
  cause problems when ported to another computer.
• Isolate any necessary implementation-dependent
  pieces.
• Use multiple level of abstraction.
• Decision factors in language selection as well as
  OS selection.
• Proper documentation identifying parts of the
  product that may be affected when porting.
• Portable data format

21
Interoperability

• Mutual cooperation of object code from different
  vendors, written in different languages and
  running on different platforms.
• Object Linking and Embedding (OLE) designed by
  MS to support compound components.
• Component Object Model (COM) use a common
  mechanism for all situations in which one
  component provides services to another component.
• Common Object Request Broker Architecture (CORBA)
  use an object request broker (ORB) that allows
  a client to invoke a method of an object,
  irrespective of where the distributed system the
  object is located.

22
Microsofts Solutions

• Object Linking and Embedding (OLE) designed by
  MS to support compound components.
• Component Object Model (COM) use a common
  mechanism for all situations in which one
  component provides services to another component.
• Every pieces of software is implemented as a COM
  component.
• Each component has one or more interfaces, each
  of which supports one or more functions.
• DCOM distributed COM.

23
OMGs Solution

• The object management Group (OMG) is a consortium
  of vendors of object-oriented technology
  currently numbering over 500.
• Common Object Request Broker Architecture (CORBA)
  an object request broker (ORB) that allows a
  client to invoke a method of an object,
  irrespective of where the distributed system the
  object is located.