Introduction to Program Design Introduction to Program Design Using Jackson Structured Programming (JSP) and Jackson Workbench

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 problem’s structure is easier to read, test and maintain Multiplication Table Example Output requirementOutput Bad Multiplication Table To make simple changes, we need to rewrite the program!simple changes Good Multiplication Table designed using JSPGood Multiplication Table designed using JSP Modifications to Good Multiplication Table are easy to make and test.Modifications to Good Multiplication Table

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

Basic JSP Method 1. Draw system diagramsystem diagram 2. Draw data structure(s) for input(s) and output(s), showing correspondencesdata structure(s) 3. Form basic program structure from data structuresbasic program structure 4. List operations needed, and allocate to form elaborated program structure List operationselaborated program structure 5. Produce structure text or program textprogram text

Using Jackson Workbench Web publishing –Structure & text –Structure diagram only Hands-on

Jackson Workbench Exercises Constructing 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

Jackson Workbench Exercises Constructing 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

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

A Short Bibliography On-line Resources: Michael Jackson Home PageMichael Jackson Home Page (articles) The Jackson Software Development Methods (Steve Ferg) My Home Page [1] Cameron, J. JSP&JSD: The Jackson Approach to Software Development. IEEE Computer Society Press. 1983, [2] Jackson, M.A. Principles of Program Design. Academic Press, New York, [3] Jackson, M.A. Constructive Methods of Program Design. In Proc 1st ECI Conference 1976, pp , Springer Verlag LNCS 44, Heidelberg (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, [5] Jackson, M.A. System Development. Prentice-Hall International, Chichester, U.K., [6] Jackson, M.A. Software Requirements and Specification. Addison-Wesley, [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 [8] Jackson, M.A. JSP in Perspective. sd&m Pioneers’ Conference, Bonn, June [9] Jackson, M.A. Problem Frames. Addison-Wesley Longman Publishing Co., Inc., [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, (Accessible at [11] Ourusoff, Nicholas. Reinvigorating the Software Engineering Curriculum with Jackson’s Methods and Ideas - ACM SIGCSE Quarterly Bulletin, June 2004.Reinvigorating the Software Engineering Curriculum with Jackson’s Methods and Ideas [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.Towards a CASE Tool for Jackson's JSP, JSD an Problem Frames

Appendix 1: About Michael Jackson (an English computer scientist, not the pop star!) Design Methods: 1. JSP (program design method) 2. JSD (systems development method) 3. Problem Frames (problem analysis and decomposition)

Appendix 1: About Michael Jackson (continued) Original ideas: 1. Design reflects problem structure 2. Begin with model of the real-world structure diagrams patterns (anticipated later work on patterns in OOAD) 3. Constructive (not top-down) Composition of models 4. Object-based (not functional) Note: See Appendix 1 & 2 for remarks on design method and methodology and for critical appraisal of JSP

Appendix 2: About JSP JSP was arguably the best program design method during the 1970’s and 1980’s. –The UK Government chose JSP as the national program design standard in 1974.[1][1] –A 1978 survey of methods concluded that JSP “is closer to a true methodology than any of the other design methodologies currently available…it is repeatable, teachable, reliable, and results in a program structure which is an excellent model of reality.”[2][2] –In 1987, ACM’s Literate Programmer column concluded that JSP leads “apparently automatically to the best structure for the program.”[3][3] JSP remains a sound method for designing the class of simple programs that read and produce serial data streams.

Appendix 3: Method versus methodology 1. 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. 2. Underlying Jackson’s methods are the following methodological principles:[1][1] 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).

Appendix 4: Jackson Workbench Jackson Workbench is a CASE tool for JSP and JSD –Keyword Computer Services Limited Version Contact: or or 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