Intro to Jackson Software Engineering

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Intro to Jackson Software Engineering

• Oct 6, 2005

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Course Preliminaries

• Course Home Page
• http//pmik.petrsu.ru/pub/ourusoff
• Use of Jackson Workbench (CASE tool) download
  JWB folder from Home Page
• Exercise(s) each class please do them and hand
  them at the start of the next class

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Reference materials

• Jacksons Home Page
• http//mcs.open.ac.uk/mj665/
• Steve Fergs Web Site
• http//www.ferg.org/jackson_methods/index.html
• Nick Ourusoffs on-line text http//www.nickshost.
  com/JSPJSDBook.zip
• Book on JSP (translated into Russian) at
  Petrozavodsk State University Library by
• D. King, Effective methods of Program Design

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Jacksons Methods

• Jackson Structured Programming (JSP)
  (1966 -1975)
• program design method for class of simple
  programs
• Principles of Program Design (1975)
• Jackson System Development (JSD)
  (early 1970s 1984)
• systems development method for dynamic systems
• System Development (1983)
• Problem Frames (1984-present)
• problem analysis and decomposition
• Software Requirements and Specification (1995)
• Problem Frames (2000)
• Span the range of software engineering
• simple programs ? information systems? problem
  description and decomposition
• Selected Papers Bibliography

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JSP

• A constructive method of design
• we construct a data structure that is the
  composition of input and output data structures
• steps are defined and at each step there are
  guidelines to check correctness of design so far
• other methods (modular programming, stepwise
  refinement) do not offer a step-by-step decision
  procedure
• modular program offers no decision procedure for
  choice of modules
• step-wise refinement offers no decision procedure
  on how to decompose moreover, the biggest
  decomposition is made at the start, before you
  know the problem
• Optimization
• Dont optimize
• If you have to, do it later
• Optimization is often unnecessary and it
  distorts the underlying structure
• Flow charts versus structure diagrams
• flow charts have been used to design programs
• a flow chart shows the flow of control, What
  happens next?, a dynamic view of a program
• Jackson tree diagram shows the static view of the
  program structure

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Program Design

• Design is about structure relation of parts to
  the whole
• Programs consist of
• elementary components operations (statements)
  in a programming language
• composite components
• sequence
• selection
• iteration

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Sequence

• (a) sequence a sequence is a composite
  component that has two or more parts occurring
  once each, in order.

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Selection

• (b) A selection is a composite component that
  consists of two or more parts, only one of which
  is selected, once.

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Iteration

• (iv) An iteration is a composite component that
  consists of one part that repeats zero or more
  times.

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Example 1

• A simple book
• A simple book consists of pages a page consists
  of lines of text a line consists of words.

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Example 2

• A more complicated book
• A 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.

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Exercises

• Draw Jackson structure diagrams for each of the
  following 
• "For lunch you may have either soup and crackers
  or a salad. You may have as many servings of
  either as you wish." 
• A conversation consists of messages, alternately
  from the user (a "user-message") and from the
  system (a "system-message"). The conversation
  always begins with a user-message and always ends
  with a system-message.
• For each of the regular expressions below,
  interpret the regular expression as a program. 
  Draw the corresponding structure diagram and give
  the equivalent Jackson structure text and pseudo
  code. 
• (a)     ((ab)c)d  (b)      (a)bcd

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Correctness of design

• Not every working program is correctly designed
• Correct design means that
• program models the real world
• a correctly designed program is
• easy to modify (90 of cost in software
  development is maintenance)
• easy to read