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4.05 - Controlled Requirements Expression


CORE or Controlled Requirements Expression is a methodology based upon the Systems Analysis and Design Technique (SADT), with a number of useful additions. This particular methodology was developed by British Aerospace in conjunction with an associated software company Systems Designers plc.

Major Steps

  • Problem Definition - a written report, with a maximum length of four pages, which precisely defines the problem.
  • Identify the hierarchy of processes involved by decomposition (as in SADT).
  • Produce a table for each process defining the flows between processes. This includes the following for each process:
    • Action
    • Input Data
    • Output Data
    • Source of data
    • Destination of Data

Tabular collection

CORE Tabular Collection

These tables help to identify flow, describe major processing functions and establish the completeness and correctness of the model.

Illustrate the data with a CORE diagram shown below:-

Basic CORE Diagram

  • Input data - data needed to perform the process
  • Output data - data created when the activity is performed
  • Control - describes the conditions that govern the transformation
  • Iteration - indicates the number of times a process is repeated and the condition that causes the process to be repeated.
  • Mechanism - the person or device that undertakes the activity

Further steps

  • Combine individual CORE diagrams so as to achieve a networked chart.
  • Undertake a constraints analysis. This should include the following for each line and box
    • What could go wrong?
    • What are the implications (causes and effect?)
    • Can it be prevented?
    • Can it be detected?
    • Is it reversible

CORE is suitable for manufacturing systems design, with its structured methodology guiding the user through all stages of an analysis, producing well documented results. It is an extension of simple input / output analysis by structuring some of the surrounding thought processes.