Goal Structuring Notation (GSN)
Learn to build safety arguments a reviewer can check: the GSN elements and rules, a construction method, modular and pattern-based arguments, confidence and defeaters, and how reviews find fallacies.
- Chapters
- 12
- Chapters
- Construction steps
- 6
- Construction steps
- Worked EPS argument
- 1
- Worked EPS argument
Quick answers
- What is GSN (Goal Structuring Notation)?
- GSN is a graphical notation for constructing and presenting safety arguments, defined by the GSN Community Standard. It expresses an argument through six core element types: Goals (claims), Strategies (the inference between claims), Solutions (evidence), plus Context, Assumption, and Justification attached sideways: connected by exactly two relationship types: SupportedBy, which carries the inference, and InContextOf, which scopes it. In automotive use, GSN structures the safety case that ISO 26262-2 requires, connecting lifecycle work products such as HARA results, FMEDA reports, and verification records into an explicit, reviewable argument that the item achieves acceptable safety.
- Does ISO 26262 require GSN?
- No. ISO 26262-2 requires a safety case: a compiled argument connecting evidence to the claim of acceptable functional safety, progressively assembled across the lifecycle and checked by a confirmation review whose independence grows with ASIL. The standard does not mandate any notation for that argument. GSN is simply the most widely adopted way to make the argument explicit, because prose safety cases collapse under the volume of work products an ASIL D item generates, hiding gaps that a structured notation exposes.
Why it pays for itself
Make safety arguments reviewable
Prose buries inference and coverage once an ASIL D item accumulates thousands of work products. GSN makes the claim-argument-evidence chain explicit enough for an assessor to read in minutes.
Build with the six-step method
Kelly's construction loop turns a blank canvas into a well-formed argument and tells you when a branch has reached the right granularity.
Scale across organizations
Modules, away elements, and contracts let one argument span OEM, supplier, and SEooC boundaries, mapping the argument structure directly onto the DIA and distributed development.
What you’ll be able to do
Write claims that can be judged
Phrase goals as propositions a reviewer can call true or false, with scope fixed by context.
Build well-formed arguments
Use the element types and relationships correctly and construct an argument with a repeatable method.
Scale arguments across teams
Use modules, contracts and patterns to split an argument across suppliers and reuse it safely.
Argue confidence
Show why the evidence deserves trust and deal openly with defeaters and counter-evidence.
Review an argument
Find fallacies and gaps in your own or someone else's GSN before an assessor does.
Chapter by chapter
- 01
Why Safety Arguments Need Structure
See why someone is owed an explicit safety argument, where prose arguments break down, and what GSN is and is not.
- Owing an argument
- Where prose breaks down
- What GSN is
- 02
The Safety Case in ISO 26262
Read what the standard asks of a safety case, who consumes it, and how it grows across item, element and supply-chain levels.
- What the standard requires
- Who reads the argument
- A living work product
- 03
The Core GSN Elements
Meet every element type, write goals that can be false, make strategies state their inference, and attach context, assumptions and justifications.
- Falsifiable goals
- Explicit strategies
- Undeveloped elements
- 04
Relationships & Well-Formed Structures
Use SupportedBy and InContextOf correctly, check connections against the permitted matrix, and recognize the common syntax errors.
- SupportedBy and InContextOf
- Permitted connections
- Common syntax errors
- 05
The Six-Step Method
Get past the blank canvas with the six-step construction loop, apply one decomposition level live, and decide when to stop.
- Six steps, one loop
- Live decomposition
- Granularity
- 06
Worked EPS Example
Build part of an electric power steering argument phase by phase, see which step produced each node, and leave honest gaps visible.
- Item and safety goal
- Phase-by-phase fragment
- Honest gaps
- 07
Modular GSN
Split a large argument into modules with away elements and contracts, and map modules onto DIA and SEooC boundaries.
- Modules and away elements
- Contracts and interfaces
- DIA and SEooC
- 08
Patterns & Reuse
Reuse argument structures through pattern notation, tour some illustrative patterns, and instantiate them with the discipline a pattern library needs.
- Pattern notation
- Illustrative patterns
- Instantiation discipline
- 09
Confidence & Defeaters
Separate the safety argument from the confidence argument, place assurance claim points, and handle defeaters and counter-evidence.
- Assurance claim points
- Three kinds of defeater
- Counter-evidence
- 10
Review & Fallacies
Learn what a GSN review checks, recognize argument fallacies in context, and practice on fragments before running a real review.
- Review scope
- Fallacy field guide
- Spot the fallacy
- 11
Tools & Alternatives
Compare GSN with other argument notations, see the SACM metamodel underneath, and pick tooling by what keeps the argument alive.
- Notation landscape
- SACM metamodel
- Tool categories
- 12
Pitfalls & Checklist
Review the recurring GSN pitfalls and what a reviewer examines first, then run a self-audit before the argument goes to assessment.
- Pitfall field guide
- Reviewer first look
- Self-audit
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Prose versus GSN
The same argument written as prose and drawn in GSN, so you can compare what each hides.
Falsifiability bench
Decide whether a statement is a claim at all before it becomes a goal.
Permitted-connections matrix
Which element may connect to which, and with which relationship.
Assurance claim points
Where confidence arguments attach to the EPS safety argument.
Spot the fallacy
Argument fragments to judge before reading the explanation.
An EPS Safety Argument Fragment
Chapter 6 builds part of the argument for an electric power steering safety goal and shows which method step produced each node.
- The item, the safety goal and the safe state being argued
- Which construction step produced which node
- The argument fragment assembled phase by phase
- Undeveloped goals left visible instead of hidden
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Who this guide is for
- Safety managers compiling a safety case toward a confirmation review
- Engineers who must turn a pile of work products into an explicit argument
- OEM and supplier teams splitting a safety case across a DIA boundary
- Reviewers and assessors judging whether an argument actually supports its claim
Frequently Asked Questions
Common questions about Goal Structuring Notation (GSN)
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Where this topic leads next.
- Verification and assessmentProven in UseISO 26262-8 Clause 14 lets you trade development evidence for statistically demonstrated field experience. This concept shows when that trade actually closes and, far more often, why it does not.
- Verification and assessmentChange Impact Analysis for Carryover & Modified SystemsMost automotive projects reuse existing systems. This page shows how ISO 26262 impact analysis and Part 8 Clause 8 change management decide what stays valid, what must be re-verified, and how to keep carryover, variants, and facelifts safe.
- Vehicle domainsActuator SafetyMotors, valves and relays are where safety goals become physical: learn how actuation channels fail stuck or runaway, how feedback and diagnostics catch it, and how safe states from de-energize to active hold are engineered and quantified.