Item Definition & Concept Phase
Learn to write the item definition that every later safety activity inherits: boundary, interfaces, assumptions, operating modes and constraints, ready for the HARA.
- Chapters
- 10
- Chapters
- Development pathways
- 3
- Development pathways
- Worked AEB item definition
- 1
- Worked AEB item definition
Quick answers
- What is an item definition in ISO 26262?
- The item definition is the first work product of the ISO 26262 safety lifecycle, required by ISO 26262-3, Clause 5. It describes the item (a system or combination of systems implementing a function at the vehicle level) before any safety analysis begins: its functionality, boundary and interfaces, operating modes and states, assumptions of use, preliminary architecture, and the legal and environmental constraints it must satisfy. Every downstream activity inherits it: the HARA derives hazards from its functions and modes, the functional safety concept builds on its boundary, and the safety case traces back to it. Errors here propagate silently, which is why it deserves a formal review before HARA starts.
- What is the difference between an item, a system, and an element in ISO 26262?
- The vocabulary comes from ISO 26262-1 and the distinctions carry real consequences. An item implements a function at the vehicle level: that vehicle-level function criterion is what separates items from everything else. A system, as the standard uses the word, joins at least three kinds of part, one that senses, one that decides and one that acts; an element is a system or part of one, down to components, hardware parts, and software units. Because an item is defined by its vehicle-level function, a Safety Element out of Context (SEooC), developed without knowing the vehicle, can never itself be an item.
Why it pays for itself
Set an unambiguous HARA scope
The item boundary decides what the hazard analysis covers. Learn to draw it explicitly (which sensors, controllers, and actuators are in, which are out) so the HARA starts clean.
Author a complete item definition
A structured template covers functions, interfaces, operating modes, assumptions of use, and legal and environmental constraints: everything ISO 26262-3 Clause 5 expects documented before hazard analysis can begin.
Catch errors while they are cheap
Defects cost roughly 1x at requirements and 10x to 100x at integration. Boundary mistakes and undocumented assumptions propagate silently into ASIL and safety-goal gaps downstream.
What you’ll be able to do
Define a clear item boundary
State what is inside the item, what is outside and which interfaces cross the line.
Write a complete item definition
Cover functions, modes, assumptions and constraints in a structure reviewers recognize.
Choose the development pathway
Decide between new development, modification and reuse, and justify the choice.
Hand a clean input to the HARA
Give the hazard analysis the functions and modes it needs to derive malfunctioning behavior.
Review before the gate
Catch the anti-patterns that propagate silently into ASILs and safety goals.
Chapter by chapter
- 01
Why It Sets Everything Up
See how the item definition seeds the whole safety lifecycle, how its errors propagate through the V-model, and what late discovery costs.
- Foundation of the lifecycle
- Error propagation
- Cost of late discovery
- 02
What Is an Item?
Work through the ISO 26262-1 vocabulary, the vehicle-level function criterion, and how an item differs from an SEooC or a combination of systems.
- Vocabulary
- Vehicle-level function
- Item versus SEooC
- 03
Contents of an Item Definition
Learn what ISO 26262-3 asks for, structure it with a template, and judge whether the definition is ready for the HARA.
- What Part 3 requires
- Structured template
- HARA readiness
- 04
Interfaces & Assumptions
Define the system boundary, the interfaces to other items, assumptions of use and preliminary architectural assumptions.
- System boundary
- Interfaces to other items
- Assumptions of use
- 05
Operating Modes & States
Capture the modes and transitions the HARA needs and see how each mode changes the exposure to a hazard.
- Mode taxonomy
- State transitions
- Modes and exposure
- 06
Legal & Environmental Constraints
Record the regulatory frameworks, environmental operating conditions and foreseeable misuse that bound the item.
- Regulatory frameworks
- Environmental conditions
- Foreseeable misuse
- 07
New vs Modified Items
Make the lifecycle initiation decision, choose between the development pathways, and scope a modification with an impact analysis.
- Lifecycle initiation
- Development pathways
- Impact analysis
- 08
From Item Definition to HARA
Use the item definition as HARA input, derive malfunctioning behaviors, and keep traceability from item to hazard to safety goal.
- HARA input
- Malfunctioning behaviors
- Traceability
- 09
Mistakes & Checklist
Recognize the anti-patterns that weaken item definitions and review a draft before it is handed to the HARA team.
- Anti-patterns
- Review checklist
- Good practice
- 10
Worked Example
Build an item definition for an automatic emergency braking system, from boundary and modes to the first hazard it enables.
- AEB item overview
- Boundary and elements
- First HARA hazard
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Expert plan pricingNot just text: the visual toolkit
Item, system, element, SEooC
The four terms that look interchangeable and are not.
Item boundary
Move the boundary and watch parts cross in and out of scope.
Assumptions of use tracker
Follow each assumption from stated to mitigated.
Operating mode state machine
Drive the modes of a steering item with events.
Same malfunction, different ASIL
How the operating mode changes the rating of one malfunction.
AEB Item Definition
The final chapter writes an item definition for an automatic emergency braking system and follows it to the first hazard the HARA can derive.
- Item overview and the vehicle-level function
- Boundary, elements and interfaces
- Assumptions and operating modes
- The first HARA hazard this definition makes possible
Unlock in course
Who this guide is for
- Engineers kicking off safety work for a new E/E vehicle function
- OEM concept teams preparing the inputs a HARA workshop needs
- Suppliers verifying the boundary and assumptions a customer item definition hands them
- Reviewers gating whether the concept phase is actually ready to start
Frequently Asked Questions
Common questions about Item Definition & Concept Phase
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Where this topic leads next.
- Concept phaseHazard Analysis & Risk Assessment (HARA)Learn how to identify vehicle-level hazards and assign ASIL ratings through Severity, Exposure, and Controllability assessment. Covers operational situations, FTTI concepts, and advanced topics for ADAS and distributed systems.
- Concept phaseFunctional Safety ConceptLearn how to derive safety goals, define safe states, and build functional safety requirements from HARA results. Covers fault reactions, degradation strategies, operating modes, and architecture diagrams with interactive videos.
- System levelTechnical Safety ConceptLearn how to translate safety goals and FSC into technical safety requirements (TSRs), system architecture, and HW/SW allocation. Covers safety mechanisms, diagnostic coverage, FMEA integration, and a complete worked example with templates.