Introduction to Program Design

1
Introduction to Program Design

• Using Jackson Structured Programming (JSP) and
  Jackson Workbench

2
Why good design is important

• There is a difference between getting a program
  to work and getting it right!
• A poorly designed program may be difficult to
  read, may not model the problem to be solved, may
  be difficult to maintain
• A program that corresponds to the problems
  structure is easier to read, test and maintain
• Multiplication Table Example
• Output requirement
• Bad Multiplication Table
• To make simple changes, we need to rewrite the
  program!
• Good Multiplication Table designed using JSP
• Modifications to Good Multiplication Table are
  easy to make and test.

3
JSP Basic Design Method

1. Draw system diagram
2. Draw data structure(s) for input(s) and
   output(s), showing correspondences, if any
3. Form basic program structure from data structures
4. List operations needed, and allocate to form
   elaborated program structure
5. Produce structure text or program text

4
Basic JSP Method

1. Draw system diagram
2. Draw data structure(s) for input(s) and
   output(s), showing correspondences
3. Form basic program structure from data structures
4. List operations needed, and allocate to form
   elaborated program structure
5. Produce structure text or program text

5
Using Jackson Workbench

• Web publishing
• Structure text
• Structure diagram only
• Hands-on

6
Jackson Workbench ExercisesConstructing Data
Structures

• A simple book consists of pages a page consists
  of lines of text a line consists of words.
• Model a simple book with a structure diagram
• Demonstration of Jackson Workbench

7
Jackson Workbench ExercisesConstructing Data
Structures(cont.)

• A regular book consists of a front and back
  cover with pages in between. Each page consists
  of lines of text each line consists of words. At
  the bottom of each page is a page number.
• Model a regular book with a structure diagram
• Demonstration of Jackson Workbench

8
Jackson Workbench Exercises Modifying basic
multiplication table

• Use JSP to design the multiplication table
• Use JSP to design the three modifications of the
  multiplication table

9
A Short Bibliography

• On-line Resources
• Michael Jackson Home Page (articles)
• The Jackson Software Development Methods (Steve
  Ferg)
• My Home Page
• 1 Cameron, J. JSPJSD The Jackson Approach to
  Software Development. IEEE Computer Society
  Press. 1983, 1989.
• 2 Jackson, M.A. Principles of Program Design.
  Academic Press, New York, 1975.
• 3 Jackson, M.A. Constructive Methods of Program
  Design. In Proc 1st ECI Conference 1976, pp
  236-262, Springer Verlag LNCS 44, Heidelberg
  1976. (Reprinted in Cameron 1983/89)
• 4 Jackson, M.A. A System Development Method.
  Tools and notions for program construction An
  advanced course Nice 1981 pages 1-25 Cambridge
  University Press, 1982.
• 5 Jackson, M.A. System Development.
  Prentice-Hall International, Chichester, U.K.,
  1983.
• 6 Jackson, M.A. Software Requirements and
  Specification. Addison-Wesley, 1996.
• 7 Jackson, M.A. The Origins of JSP and JSD a
  Personal Recollection. IEEE Annals of Software
  Engineering Volume 22 Number 2, pages 61-63, 66,
  April-June 2000.
• 8 Jackson, M.A . JSP in Perspective. sdm
  Pioneers Conference, Bonn, June 2001.
• 9 Jackson, M.A. Problem Frames. Addison-Wesley
  Longman Publishing Co., Inc. , 2001.
• 10 Ourusoff, Nicholas. Using Jackson Structured
  Programming (JSP) and Jackson Workbench to Teach
  Program Design. (Proceedings of 2003 Informing
  Science and Information Technology Education,
  Pori, Finland, June 24-27, 2003. (Accessible at
  http//ecommerce.lebow.drexel.edu/eli/2003Proceedi
  ngs/PaperPage106.html)
• 11 Ourusoff, Nicholas. Reinvigorating the
  Software Engineering Curriculum with Jacksons
  Methods and Ideas - ACM SIGCSE Quarterly
  Bulletin, June 2004.
• 12  Ourusoff, Nicholas. Towards a CASE Tool for
  Jackson's JSP, JSD an Problem Frames - 1st
  International Workshop on Applications and
  Advances in  Problem Frames, ICSE May 24, 2004.

10
Appendix 1 About Michael Jackson

• (an English computer scientist, not the pop
  star!)
• Design Methods
• JSP (program design method)
• JSD (systems development method)
• Problem Frames (problem analysis and
  decomposition)

11
Appendix 1 About Michael Jackson (continued)

• Original ideas
• Design reflects problem structure
• Begin with model of the real-world
• structure diagrams
• patterns (anticipated later work on patterns in
  OOAD)
• Constructive (not top-down)
• Composition of models
• Object-based (not functional)
• Note See Appendix 1 2 for remarks on design
  method and methodology and for critical appraisal
  of JSP

12
Appendix 2 About JSP

• JSP was arguably the best program design method
  during the 1970s and 1980s.
• The UK Government chose JSP as the national
  program design standard in 1974.1
• A 1978 survey of methods concluded that JSP is
  closer to a true methodology than any of the
  other design methodologies currently availableit
  is repeatable, teachable, reliable, and results
  in a program structure which is an excellent
  model of reality.2
• In 1987, ACMs Literate Programmer column
  concluded that JSP leads apparently
  automatically to the best structure for the
  program.3
• JSP remains a sound method for designing the
  class of simple programs that read and produce
  serial data streams.

13
Appendix 3 Method versus methodology

• The distinction between method and methodology is
  often blurred. According to Jackson, a method is
  a way of doing something, whereas a methodology
  discusses the principles of one or more methods.
• Underlying Jacksons methods are the following
  methodological principles1
• Easier decisions should be made before difficult
  decisions.
• Error-prone decisions should be deferred.
• Implicit decisions should be avoided.
• Error-prone decisions should be subjected at the
  earliest possible moment to confirmation or
  refutation.
• Whenever possible, decisions should be
  independent of each other (orthogonal).

14
Appendix 4 Jackson Workbench

• Jackson Workbench is a CASE tool for JSP and JSD
• Keyword Computer Services Limited. 2002. Version
  2.04. Contact KCSL_at_BTInterent.com or
  Jim.Newport_at_BTInternet.com or 44 1494 870427
• Structure Editor
• intuitive editing via hot spot images that
  appear at different locations on a tree structure
  diagram indicating an operation that can be
  performed at that point simply by left-clicking
• Generates code (C, Java, Visual BASIC, COBOL)
  and documentation
• Under development
• JSP works well JSD not complete