Goal Structuring Notation (GSN)
Goal Structuring Notation is an argumentation notation developed at the
University of York. Further details and publications about the GSN methodology
can be found at the GSN Club.
ASCE is the most widely used commercial tool for GSN.
As described on the GSN Club site, the
purpose of a goal structure in GSN is:
"The principal purpose of any goal structure is to show how
goals (claims about the system) are successively broken down into sub-goals
until a point is reached where claims can be supported by direct reference
to available evidence (solutions). As part of this decomposition, using the
GSN it is also possible to make clear the argument strategies adopted (e.g.
adopting a quantitative or qualitative approach), the rationale for the
approach and the context in which goals are stated (e.g. the system scope or
the assumed operational role)."
The principal node types in GSN are as follows:
Goal - a statement or claim asserted within the argument that can
be assessed to be true or false,
- "System X is adequately safe during the shut down phase of
- "Unit testing is complete"
- "All identified hazards are adequately managed in the hazard
- "Design personnel are suitably qualified"
- "Training materials have been reviewed"
Each goal (claim) is supported by (solved by) by a number of sub goals,
strategies or solutions.
Strategy - a description of the argument approach
presented in support of a goal. e.g.:
- "argue by considering safety of subsystems"
- "because wiring conforms to relevant electrical standards"
This element is optional, but often it is good practice to include to
explain the approach to satisfying the parent claim
If the approach to
solving a goal is
straightforward or well understood by the intended audience, it is permissible to simply link directly
Solution - a reference to the evidence being presented in
support of the goal or strategy, e.g.
- "the hardware reliability analysis report"
- "interlock design documentation"
Usually the solution node will summarise and link out to the relevant
report containing the evidence
ASCE contains a number of tools to
- linking to, management and tracking of changes in the underlying
Context - Contextual material to define terms used, or the
operational context for the system being argued for
Assumption - A supporting proposition that does not have
support in this argument
Explicit assumptions can be used to indicate uncertainty or where the
scope resolution for some claim is addressed by another party
Justification - A reason or justification that the adopted
strategy is being adopted
For example, a standard might require a certain approach to supporting
the claim being made.