Programming and Software Engineering

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Programming and Software Engineering
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Software Development

• We can define two main classes of software
• User-written software
• solve a particular problem, access information,
  automate routine tasks
• this has been a traditional approach for
  engineers
• availability of powerful applications software
  has greatly reduced the need for users to write
  programs
• Commercial software
• software written for commercial distribution, or
  for the use of other people within an organization

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Software Complexity and Software Engineering

• Comparing simple user-written programs to
  commercial applications is like comparing a
  birdhouse to the Skydome
• For example, software for the space shuttle
  consists of over 40 million lines of code!

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The State of the Software Industry

• Software is one of the most important industries
  in the world
• Although the applications are high tech, software
  companies are still run like cottage industries
• Software is manufactured today the same way the
  first automobiles were manufactured 100 years ago!

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Software Manufacturing Methods

• Each program is built from scratch by skilled
  craftspeople
• The components must be carefully adjusted for the
  whole thing to work
• Parts or components are not interchangeable
  between programs (or cars in 1900)
• There are few standards

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Critical Problems

• Software takes too long to develop
• Productivity is low
• There are many bugs that are difficult to fix
• Much effort is directed to reinventing the wheel
  (e.g., creating user interfaces)
• Programmers must be highly skilled

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Software Engineering

• Designing a software system is as complex as
  designing a rocket, a large building, or a car.
• Designing software systems requires a sound
  engineering methodology
• Currently, most programmers are not trained or
  certified as engineers
• Software engineering has become an important
  discipline

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Critical Labour Shortage

• There is a critical shortage of programmers and
  other information technology professionals
• Very few engineering schools offer programs in
  software engineering
• Western will have one of the first software
  engineering programs in Canada

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Software Life Cycle

• The software life cycle consists of several
  phases, starting with identification of a need,
  and ending only when the software is no longer in
  use
• The software life cycle is similar to the life
  cycle of any manufactured or engineered product

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Software Life Cycle (summary)

• Identify and describe an application
• Analyse the application in detail
• Preliminary design
• Detailed design
• Coding
• Testing and debugging
• Documentation and maintenance

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Software Life Cycle

• Identify and describe an application
• market and user surveys
• brainstorming
• conceptual design
• Analyse the application in detail
• identify the functional modules

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Software Life Cycle

• Preliminary design
• describe the general software structure using
  flowcharts or pseudocode
• design alternatives can be explored at this stage
• Detailed design
• completely specify the program logic
• Coding
• implement the design using a programming language
• coding from a detailed design is like building a
  house from a blueprint

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Software Life Cycle

• Test and debug
• errors can be due to syntax (ie, incorrect
  grammar), or logic
• logic errors are very difficult to detect
• Documentation and maintenance
• software may remain in use for years
• someone must continue to fix bugs, add features,
  and help users
• the cost of maintenance can be much higher than
  the cost of development

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Programming Languages

• Assembly language
• High-level languages
• FORTRAN, C, Pascal
• Fourth-generation languages (4GLs)
• Very high-level languages
• application generators
• natural language

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Assembly Language

• Much software is still written in assembly
  language
• Advantages
• speed, compactness, efficiency
• Disadvantages
• not portable
• difficult to implement and debug
• every function must be programmed at machine
  level
• Thousands of programs written in Intel 80x86
  assembly language will not run on any other
  processor

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High-level Languages

• Most software is written in high level languages
• Fortran, Pascal, Basic and C are popular
• C has become a de facto standard for several
  reasons
• standards exist, so the code is portable
• it has much of the power and flexibility of
  assembly language

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Problems with these Languages

• Difficult to learn and use
• The only built-in I/O support is character-based
  read and write
• Not suitable for occasional quick and dirty
  programming
• Development of Graphical User Interface is
  difficult
• Much of the code is a reinvention of the wheel

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Fourth Generation Languages (4GLs)

• 4GLs and Rapid Application Development (RAD)
  tools are used to develop applications with
  little or no programming
• Typically use a graphical, drag-and-drop approach
• Corresponding source code is generated
  automatically

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Examples of RAD Tools

• Microsoft Visual Basic
• Borland Delphi
• Powersoft PowerBuilder
• Topspeed Clarion

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Structured Programming

• An important methodology for dealing with
  complexity is structured programming
• Complex tasks need to be broken down into simpler
  subtasks
• Structured programming reduces complex problems
  to collections of simple, interconnected modules
• It is up to the programmer to implement
  structured programming

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Programming for DOS

• DOS provides few system services to the
  programmer
• It is up to the programmer to implement the
  following modules for each application from
  scratch
• user interface
• printer drivers
• video drivers
• etc.
• As a result, every application looks and works
  differently

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Programming for Windows

• Windows provides many standard services to the
  programmer
• It also specifies a common look and feel for all
  applications
• Now the programmer does not need to worry about
  low level drivers, GUI programming, etc.
• The programs call Windows Application Program
  Interface (API) functions
• Unfortunately, the programmer needs to be
  knowledgeable about hundreds of API functions

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Graphical User Interfaces

• In most applications, the majority of code is
  associated with the user interface
• The Windows API provides hundreds of functions to
  create menus, dialog boxes, etc.
• Developing the GUI is difficult

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Procedural Vs. Interactive, Event-driven Programs

• Traditional programs are procedural, with limited
  user interaction
• Most Windows applications are event-driven
• The program responds to user events, like menu
  selections, keyboard input and mouse clicks

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Hello, World!

• A classical C programming example simply prints
  the message Hello, world on the screen.
• In standard C, the entire program is shown below.

include ltstdio.hgt main() printf(Hello,
world\n)
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Hello, World!

• The equivalent program in Windows requires two
  pages of cryptic code
• The program creates a window, and writes Hello,
  Windows in the centre
• This is the simplest Windows program possible
• This example demonstrates the shift from
  text-based applications to event-driven graphical
  applications

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Hellowin.c Page 1
/------------------------------------------------
-------- HELLOWIN.C -- Displays "Hello,
Windows" in client area (c)
Charles Petzold, 1992 --------------------------
------------------------------/ include
ltwindows.hgt long FAR PASCAL _export WndProc
(HWND, UINT, UINT, LONG) int PASCAL WinMain
(HANDLE hInstance, HANDLE hPrevInstance,
LPSTR lpszCmdParam, int nCmdShow)
static char szAppName "HelloWin"
HWND hwnd MSG msg
WNDCLASS wndclass
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Hellowin.c Page 2
if (!hPrevInstance)
wndclass.style CS_HREDRAW CS_VREDRAW
wndclass.lpfnWndProc WndProc
wndclass.cbClsExtra 0
wndclass.cbWndExtra 0
wndclass.hInstance hInstance
wndclass.hIcon LoadIcon (NULL,
IDI_APPLICATION) wndclass.hCursor
LoadCursor (NULL, IDC_ARROW)
wndclass.hbrBackground GetStockObject
(WHITE_BRUSH) wndclass.lpszMenuName
NULL wndclass.lpszClassName
szAppName RegisterClass (wndclass)

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Hellowin.c Page 3
hwnd CreateWindow (szAppName, //
window class name "The Hello Program",
// window caption
WS_OVERLAPPEDWINDOW, // window style
CW_USEDEFAULT, // initial x
position CW_USEDEFAULT,
// initial y position
CW_USEDEFAULT, // initial x size
CW_USEDEFAULT, // initial
y size NULL,
// parent window handle
NULL, // window menu handle
hInstance, //
program instance handle NULL) //
creation parameters
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Hellowin.c Page 4
ShowWindow (hwnd, nCmdShow) UpdateWindow
(hwnd) while (GetMessage (msg, NULL, 0,
0)) TranslateMessage (msg)
DispatchMessage (msg)
return msg.wParam long FAR PASCAL
_export WndProc (HWND hwnd, UINT message, UINT
wParam,
LONG lParam) HDC
hdc PAINTSTRUCT ps RECT rect
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Hellowin.c Page 5
switch (message) case
WM_PAINT hdc BeginPaint (hwnd, ps)
GetClientRect (hwnd, rect)
DrawText (hdc, "Hello, Windows!", -1,
rect, DT_SINGLELINE DT_CENTER
DT_VCENTER) EndPaint (hwnd, ps)
return 0 case
WM_DESTROY PostQuitMessage (0)
return 0 return
DefWindowProc (hwnd, message, wParam, lParam)

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GUI Development Tools

• Interactive tools have appeared to allow the
  programmer to design and test the GUI graphically
• The code is automatically generated to implement
  the GUI
• This saves much time, especially for
  inexperienced programmers

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Object-Oriented Programming (OOP)

• Traditional languages treat data and procedures
  as separate entities
• The programmer designs procedures (instructions)
  to manipulate data (variables, files, etc.)

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Object-Oriented Programming (OOP)

• Object-Oriented languages treat programs as a
  collection of objects
• An object is a combination of data and procedures
  that are stored together as a reusable unit
• Objects communicate by sending messages to each
  other

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Object-Oriented Programming (OOP)

• A powerful feature of OOP is inheritance
• New objects can be based on existing objects,
  with just minor changes
• Groups of similar objects can be grouped into
  classes

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Object-Oriented Programming (OOP)

• Each member or instance of a class contains
  shared code, plus code specific to the instance
• For example, each open window in Windows is an
  instance of a class of window objects
• Methods for opening, closing, moving, resizing,
  etc. are shared by all instances

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Advantages of OOP

• Generic objects can be reused in many
  applications
• This reuse of software encourages a building
  block approach to software development, using
  standardized parts
• Software development is much faster
• Software is easier to understand, debug and
  maintain

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Disadvantages of OOP

• Difficult to learn for programmers used to
  procedural languages
• A new way of thinking is required
• Objects reduce portability of code

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Object-Oriented Languages

• The major OOP language is C
• C is standard C with object-oriented extensions
• Another OOP language is Smalltalk
• A brand-new alternative is Java

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Component Software

• Software reuse can be accomplished using
  component software
• Example Microsoft Component Object Model (COM)
  and ActiveX
• Existing ActiveX components can be incorporated
  into new applications, saving much development
  time

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Java

• Announced by Sun Microsystems in 1995
• Greatly hyped!
• Seen as a way to compete with the Wintel duopoly
• Issues have been political, as well as technical

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The Java Promise...

• Embedded applications like set-top boxes and
  cellular phones
• Internet applications
• Network computers
• Platform-independent software development

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What is Java?

• A new language, similar to C but without the
  drawbacks
• built-in garbage collection
• no pointers
• bounds checking
• Object oriented from ground up
• The language improvements eliminate many sources
  of bugs

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Write Once, Run Anywhere

• Java includes standard libraries for graphical
  interfaces, etc.
• Java programs run inside a Virtual Machine (VM)
• They are independent of processor or operating
  system

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Applets and Network Software

• Java can be used to write normal programs, or
  applets that run inside a Web browser
• Applets are downloaded from a server before
  running
• The Network Computers being promoted by Sun,
  Oracle and others will run Java

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Java Applets
Virtual Machine
Server
Applet
Browser
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The Hype and the Reality

• Sun is trying to enforce 100 Pure Java that
  will run on any certified VM
• Microsoft and others are extending and modifying
  Java
• Visual J makes use of Windows capabilities
• not portable
• Microsoft, Netscape and others have developed
  their own flavours of the VM
• The Java specification continues to change

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The Trade-offs

• Pure Java
• Runs on any platform
• Lowest common denominator
• Limited development tools
• Performance not optimized

• Proprietary Java
• May be platform-specific
• Makes use of features of underlying operating
  system
• Good development tools
• Optimized performance

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User-Oriented Languages

• Easy to use programming applications have emerged
  to meet the need of end-user programming
• A good example is Microsoft Visual Basic
• Users with limited programming experience can
  quickly develop powerful, professional-looking
  applications with full graphical interfaces.

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Macros and Application Customization

• Many useful applications can be created by
  building on existing software
• Word and Excel can be extensively programmed
  using Visual Basic for Applications
• For example, you could create a program to accept
  data using an input form, analyze the results,
  and plot a graph, all in Excel

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Computer Aided Software Engineering (CASE)

• CASE is a set of productivity tools for
  programmers and software developers
• The tools are analogous to wordprocessors and
  spreadsheets for business people
• CASE is still immature, but will become
  increasingly important in the future

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Computer Aided Software Engineering (CASE)

• The CASE toolkit includes
• Design tools
• flow diagrams, structure charts, etc.
• Prototype tools
• user interface, screen generators, report
  generators
• Information repository tools
• database for the software development project

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Computer Aided Software Engineering (CASE)

• Program development tools
• organize, generate and test code
• Methodology tools
• support standard development methodology