Program Design Process

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Program Design Process

• Carl Smith
• National CertificateYear 2 Unit 4

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Unit 4 objectives

• Apply simple analysis and design techniques to
  the software development process.
• Develop basic high-level code using an
  appropriate procedural programming language.
• Use suitable testing methods to ascertain the
  correctness of a working piece of code.
• Produce appropriate documentation for a given
  program application.

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The Vision

• Its all about vision. A complex system comes
  into being when someone has a vision of how new
  technology can make things better. Developers
  have to fully understand the vision and keep it
  firmly in mind as they create the system that
  realises the vision.
• Schmuller Joseph, 2001, Teach yourself UML in 24
  hours , SAMS 2nd Edition

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Feasibility studies

• The development of an IT system usually happens
  when someone has a problem which they hope will
  be solved by the introduction of such a system. I
  shall refer to the person who has the problem as
  the system sponsor.
• It is normal and sensible to begin with a
  feasibility study to establish whether the
  sponsors idea is a non-starter this should
  happen with any new project in any area of work,
  not just computing.

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Feasibility studies 2

• It may involve no more than the sponsor and some
  representative's) of the IT department (probably
  a systems analyst) having a discussion, or it may
  require investigative action by sponsor or
  analyst or both.
• The end product will be a feasibility study
  report, which is a plain English document stating
  whether or not the proposed system development is
  feasible (i.e. possible).

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Feasibility studies - 3

• In practice this answer is usually yes because
• all things are possible given sufficient time,
  energy and resources
• although time, energy and resources are always
  limited in practice, the sponsor (who has been
  dreaming of a better future) will moderate
  demands until the project is feasible
• if IT departments dont develop new computer
  systems what else are they going to do?
• Often the feasibility study report will identify
  actions that need to be taken before the new
  system can be developed (e.g. ensuring every user
  has their own networked PC).

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Requirements Specification

• Once the new system development is approved, the
  next task is usually to produce a document called
  the requirements specification.
• This is an exhaustive list of the requirements
  the users have of the new system. It can take a
  long time to create, and tends to end up as a
  substantial document. It should deal in detail
  with
• what the users want the new system to do
  (referred to as the functionality of the system)

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Req Spec 2

• data formats (e.g. that personnel numbers are of
  the form X123456, department codes look like
  FIN or PER, and rooms are coded FIN012 or
  PER306)
• what reports the new system should produce
• response times, data security, user access
  levels, backup procedures, and lots more.
• The modern tendency is to produce enterprise
  systems which integrate all the tasks an
  organisation does, so the users will be at all
  levels of the organisation (managing director,
  accountant, departmental heads, secretaries,
  receptionists, etc.). Each of these categories of
  user will have different requirements.

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System or Technical Specification

• Once produced, the requirements specification
  (commonly called the req spec) is handed to
  systems analyst(s) who scrutinise the
  requirements and work to design the new system.
  Their output may include-
• Dataflow Diagrams (DFDs)
• A Data Dictionary (DD)
• Process Specifications
• Entity-Relationship Diagrams (ERDs)
• State-Transition Diagrams (STDs)
• Structure Charts
• Flow Charts
• Pseudo Code
• JSP Diagrams

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Technical Spec - 2

• Project managers may be drawing up PERT charts
  and Gantt charts.
• Of particular interest will be program
  specifications which the systems analyst produce.
  These are handed to programmers for coding. (You
  can think of the questions in the Assignments as
  your program specifications.)
• The entire output of the design stage is termed
  the system (or technical) specification and is
  invariably referred to as just the spec.

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Program Design Methods

• Functional Decomposition
• JSP
• Pseudo Code
• Flow Charts
• Object Oriented Design

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Functional Decomposition

• This method focuses on the functions that the
  program has to carry out
• We express the problem solution in terms of a
  sequence of actions
• E.g. Making a cup of tea,
• Changing a car tyre

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Functional Decomposition

• FD uses pseudo code to express the solution
• E.g.
• Switch on kettle
• While water is not boiling DO
• Whistle a tune
• End While
• Switch off kettle

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Functional Decomposition

• What about data?
• Data is not considered in that this method
  concentrates on what the program should do NOT
  what data is needed
• The data is considered when we know what
  operations are to be performed
• It is a TOP-DOWN method sometimes called
  Step-Wise Refinement

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JSP

• Jackson Structured Programming named after
  Michael Jackson..!
• Unlike FD, JSP should match the structure of a
  file or files that the program should work on
• Examples

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JSP

• Consists of five clearly defined steps
• 1)
• 2)
• 3)
• 4)
• 5)

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• Diagrams
• Own version of pseudo code - PDL

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Flow Charts
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Flow Charts
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Object Oriented Design
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Summary

• We covered-
• National Certificate Unit 4 objectives
• The stages of program design
• Some Design methods in use
• Any Questions?