Influence diagrams

An influence diagram represents the main structural feature of a system and the important influences that exist between them. It presents an overview of areas of activity, organisation and other groupings, and their main interconnections. It is used to explore those interconnections, possibly leading to redefinition of the components and new views on how they influence each other.

The elements of influence diagrams are blobs labelled by words and arrows between the blobs showing which parts of the system influence others. Ideally, the arrows are labelled saying what the influence of one component on another is.

The rules for drawing influence diagrams are:

• when they are present blob lines represent component boundaries;
• an arrow between components denotes influence or possible influence;
• arrows do not show material flows;
• like a system map, an influence diagram is a snapshot, not a sequence in time.

The guidelines for using influence diagrams are:

• arrows from features in the environment should terminate at an internal system component, not at the system boundary;
• different line weights can denote the strength of influence;
• where influence is two-way, two separate arrows should be used rather than a double-headed arrow, since the influences may be different;
• resist the temptation to overload the diagram with information;
• space and relative difference can be used to suggest things about the nature of the relationship, e.g. important but distant.