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Slide 8.1

The McGraw-Hill Companies, 2002

Object-Oriented and Classical Software

Engineering

Fifth Edition, WCB/McGraw-Hill, 2002

Stephen R. Schachsrs@vuse.vanderbilt.edu

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Slide 8.2

The McGraw-Hill Companies, 2002

CHAPTER 8

REUSABILITY,PORTABILITY, AND

INTEROPERABILITY

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Slide 8.3

The McGraw-Hill Companies, 2002

Overview

q Reuse conceptsq Impediments to reuseq Reuse case studiesq Objects and reuseq Reuse during the design and implementation

phasesq Reuse and maintenanceq Portabilityq Techniques for achieving portabilityq Interoperability

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Slide 8.4

The McGraw-Hill Companies, 2002

Reuse Concepts

q Two types of reuse Accidental reuse

First, product is built Then, parts put into part database for reuse

Planned reuse First, reusable parts are constructed Then, products are built using these parts

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Slide 8.5

The McGraw-Hill Companies, 2002

Why reuse?

q Minor Reason It is expensive to design, implement, test, and

document software Only 15% of new code serves an original purpose

(average)

Reuse of parts saves Design costs Implementation costs Testing costs Documentation costs

q Major Reason Maintenance

q Maintenance consumes two-thirds of software

cost

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Slide 8.6

The McGraw-Hill Companies, 2002

Impediments to Reuse

q Not invented here (NIH) syndromeq Concerns about faults in potentially

reusable routinesq Storageretrievalq Cost of reuse

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Slide 8.7

The McGraw-Hill Companies, 2002

What sort of reuse rates can we expect?

q Theoretical maximum is 85%q What can we get in practice?q Consider case studies (1975 through 2000)

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Slide 8.8

The McGraw-Hill Companies, 2002

Raytheon Missile Systems Division

q Data-processingsoftware

q Planned reuse of Designs

6 code templates COBOL code

3200 reusablemodules

q

Reuse rate 60%(19761982)

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Slide 8.9

The McGraw-Hill Companies, 2002

Toshiba Fuchu Works, Tokyo

q Industrial process control systemsq Accidental reuse of

Specifications Designs Modules Contracts Manuals Standards

q

Reuse rate (1985)q 33% designq 48% code

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Slide 8.10

The McGraw-Hill Companies, 2002

NASA Software

q Ground support system for unmannedspacecraft control

q Management permitted (but did not encourage)accidental reuse

q Accidental reuse of Modules

q Reuse rate (1982) 28% reused unchanged 10% reused with minor changes

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Slide 8.11

The McGraw-Hill Companies, 2002

GTE Data Services

q Data-processing softwareq Strongly encouraged by management

Cash incentives when module was accepted for reuse Cash incentive when module was reused

q Accidental reuse of Modules

q Reuse rate

(1988) 15% reused code, $1.5 million saved (est. 1989) 20% reused code (est. 1993) 50% reused code

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Slide 8.12

The McGraw-Hill Companies, 2002

Hewlett-Packard

q Implemented in many divisions of thecompany

q Software Technology Division Accidental reuse of resource planning software 4.1 faults per KLOC of new code, 0.9 for reused

code Overall fault rate decreased 51% Productivity increased 57% Cost $1 million, savings $4.1 million (198392)

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Slide 8.14

The McGraw-Hill Companies, 2002

European Space Agency

q Ariane 5 rocket blew up 37 seconds after lift-off q Cost: $500 millionq Reason: attempt to convert 64-but integer into 16-

bit unsigned integer, without Ada exception handler

q On-board computers crashed, so did rocketq Conversion was unnecessary

Computations on the inertial reference system can stop

9 seconds before lift-off But, if there is a subsequent hold in countdown, it takesseveral hours to reset the inertial reference system

Computations therefore continue 50 seconds into flight

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Slide 8.15

The McGraw-Hill Companies, 2002

European Space Agency (contd)

q Cause of problem Ten years before, it was mathematically proven that

overflow was impossibleon the Ariane 4 Because of performance constraints, conversions that

could not lead to overflow were left unprotected

Software was used, unchanged and untested, onAriane 5 But, the assumptions for the Ariane 4 no longer held

q Lesson

Software developed in one context needs to beretested when integrated into another context

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Slide 8.16

The McGraw-Hill Companies, 2002

Size of Reused Components

q NASA Most reused components were small

q Toshiba Many large components were reused

q

GTE Many large components were reused

q Reason

A strong managerial commitment for reuse is needed

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Slide 8.17

The McGraw-Hill Companies, 2002

Objects and Reuse

q Claim of CS/D Ideal module has functional cohesion

q Problem The data on which the module operates

q

We cannot reuse a module unless thedata are identical

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Slide 8.20

The McGraw-Hill Companies, 2002

Library or Toolkit

q Set of reusable routinesq Examples:

Scientific software GUI class library or toolkit

q The user is responsible for the control logic (white infigure)

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Slide 8.22

The McGraw-Hill Companies, 2002

Design Pattern

q A solution to ageneral designproblem

q In the form of a set

of interactingclassesq The classes need

to be customized(white in figure)

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Slide 8.23

The McGraw-Hill Companies, 2002

Widget Generator

q Tool that uses theset of classescreated by thewidget generator

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Slide 8.24

The McGraw-Hill Companies, 2002

Abstract Factory Pattern

q Abstract classesand abstract(virtual) methods

q The interfacesbetween client andprogram andgenerator areabstract

q The applicationprogram isuncoupled from thespecific operatingsystem

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Slide 8.25

The McGraw-Hill Companies, 2002

Software Architecture

q Encompasses a wide variety of designissues, including: Organization in terms of components How those components interact

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Slide 8.26

The McGraw-Hill Companies, 2002

Reuse of Software Architecture

q Architecture reuse can lead to large-scale reuseq One mechanism:

Software product linesq Case study:

Hewlett-Packard printers (1995 to 1998) Person-hours to develop firmware decreased by a factor of 4 Time to develop firmware decreased by factor of 3 Reuse has increased to over 70% of components

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Slide 8.27

The McGraw-Hill Companies, 2002

Reuse and Maintenance

q Reuse impacts maintenance more than developmentq Assumptions

30% of entire product reused unchanged 10% reused changed

q Savings during maintenance are nearly 18%q Savings during development are about 9.3%

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Slide 8.28

The McGraw-Hill Companies, 2002

Objects and productivity

q Reuse achieved Not via modules with functional cohesion, but via objects (informational cohesion)

[classes]q In general

Software costs have decreased Overall quality has improved Large products are essentially collection of

smaller products

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Slide 8.29

The McGraw-Hill Companies, 2002

Difficulties and Problems

q Learning curve Particularly noticeable with GUI

q Problems with inheritance New subclass does not affect its superclass

But, any change to a superclass affects all itssubclasses Subclasses low in the inheritance tree can be huge

(inherited attributes)

q Polymorphism and dynamic binding Maintenance problems were already discussed

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Slide 8.30

The McGraw-Hill Companies, 2002

Difficulties and Problems (contd)

q Advantages far outweigh the problems Numerous refereed (e.g., [Capper et al., 1994]) and

informal (OOPSLA Addendum) reports

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Slide 8.31

The McGraw-Hill Companies, 2002

Portability

q Product P: Machine M 1 Op. Sys. O 1 Compiler C 1q Need P': Machine M 2 Op. Sys. O 2 Compiler C 2q P is portable if it is cheaper to port P than to write

P' from scratch

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Slide 8.32

The McGraw-Hill Companies, 2002

Incompatibilities

q Hardware (disk, tape, characters, parity)q Operating system (JCL, virtual memory)q Numerical software (word size, Ada)q Compiler

FORTRAN Pascal COBOL C Ada C++ Java

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Slide 8.33

The McGraw-Hill Companies, 2002

Why Portability?

q Difficulties hamperingportability One-off software Hardware incompatibility Lifetimes of software, hardware Multiple copy software

q Portability saves money!

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Slide 8.36

The McGraw-Hill Companies, 2002

Portability Strategies (contd)

q Portable data COBOL, Pascal versus ASCII files DBMS

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Slide 8.37

The McGraw-Hill Companies, 2002

Interoperability

q The mutual cooperation of object code From different vendors Written in different languages Running on different machines

q

Example: Nation-wide network of ATMs Server runs database software Clients (ATMs) run C++

Communications software Security

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Slide 8.38

The McGraw-Hill Companies, 2002

COM

q Common Microsoft mechanism for allcomponent services Within the same process

Invocation

Different processes on the same machine Interprocess communication

Between different machines Remote process call (RPC)

l d

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Slide 8.39

The McGraw-Hill Companies, 2002

How COM Is Implemented

q Each piece is implemented as a COMcomponent (object)

q Each component has one or more interfacesq Each interface supports one or more functions

(methods)q The client calls the COM library and specifies

The class of the component The specific interface

q

The COM library instantiates the COMcomponent

W i

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Slide 8.40

The McGraw-Hill Companies, 2002

Warning

q COM uses object-oriented terminology Class Object Method

q

However, COM is currently only object-based, not object-oriented

CORBA

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Slide 8.41

The McGraw-Hill Companies, 2002

CORBA

q International standard architecture for object-oriented systems

q Object request broker (ORB) allows client toinvoke a method of any object in the system

q The mother of all client/server middleware

C i COM d CORBA

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Slide 8.42

The McGraw-Hill Companies, 2002

Comparing COM and CORBA

q CORBA is an international standard Implemented on a wide variety of platforms

q COM is a Microsoft product Hard to use with non-Microsoft products

q Integration of COTS software is easier with COM Most COTS software is supplied by Microsoft

q CORBA is much simpler than COM

F T d i I bili

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Slide 8.43Future Trends in Interoperability

q COM and CORBA are currently the big twoq Other interoperability products may succeed,

such as JavaBeansq Web-based applications need to be integrated

into clientserver productsq XML (Extensible Markup Language) will probably

play a major role