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4.02 - Techniques of Systems Analysis


There are number of techniques commonly used to analyse and design systems. In general, the simpler the technique the better it is. The use of standard input-output diagrams and flow chart symbols facilitates ease of communication and discussion by multi-skilled teams.

Informal techniques - the techniques based upon natural language are probably the most widely used as it requires no special skills beyond a basic command of a natural language. However, it is probably the most unsuitable for systems of any complexity, due to its ambiguity.

Formal Techniques - such as Higher Order Systems Methodologies - are based upon the use of formal mathematical notation and theorems. Whist being precise, they are of limited use due to the high degree of skill required for their application and the high levels of complexity typical of most manufacturing systems.

Special Input Techniques - these are techniques that employ specially designed languages or input formats in computerisation of a specification.

Diagrammatic Structured Analysis Techniques - These techniques, where diagrams are employed to convey the information necessary for systems, are of great use. Whilst requiring a reasonable skill level, they can be used for a wide variety of applications to aid structured thinking.

Diagrammatic Structured Analysis Techniques

Manufacturing systems are often complex and difficult to specify, analyse, understand and design. In an attempt to order the complexity of the design task, and to increase the possibly of problem comprehension, the concept of “Structured Analysis” was introduced.

The basic philosophy of structured analysis and design techniques is that problems, (or systems), can be decomposed into smaller elements, allowing the whole problem to be seen at the same time as its more detail constituent parts. This decomposition can be carried out until the limit of usefulness has been reached, when no more can be gained by further analysis.

Decompose complex information into smaller data blocks

In this way the complexity of the problem is “ordered” so as to provide clarity. Not only are structured analysis techniques helpful in analysis and design, due to the consistency of documentation, they are also invaluable, generally in the area of communication of information.

Process Flow Charts

Used to define in detail the linked sequence / mix of value added and non-value-added activities that make up a process or natural group contained within a box in an input / output diagram. These are standard symbols used internationally varying from classical work study symbols (circle, square, triangle, arrow, D) to chemical process plant symbols.

Input / Output Analysis

Input / output analysis is a method of generating all possible ingredients to give all possible results.




The process is first defined, desirable outputs and necessary inputs detailed. Sub-systems are then carefully matched together by connecting inputs and outputs at interfaces. (See Guide Section 4.03)

Structured Analysis and Design Technique (SADT)

SADT was the forerunner of many of the structured analysis techniques and is based around the maxim:

"Everything worth saying about anything worth saying something about, must be expressed in six or fewer pieces."

In essence the technique is an enhancement of the simple input / output technique. In addition to simple inputs and outputs, controls (why something is done) and mechanisms (how something is done are shown on the models, or process representation that are generated (See Guide section 4.04).

Controlled Requirements Expression (CORE)

CORE is a methodology based upon SADT, with a number of useful additions. These additions include the explicit inclusion of a section for problem definition and procedural stages for ensuring that models are logical, well documented and easy to follow (See Guide Section 4.05).

To summarise, structured methodologies are of assistance in the following areas:

  • The ordering of complexity
  • The improvement of communication in specification, analysis and design
  • The standardisation of documentation
  • The review, correctness and completeness check procedures associated with systems
Further Reading