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Effective Requirements Writing – Avoiding Ambiguous Requirements
Published April 21, 2023

Effective Requirements Writing – Avoiding Ambiguous Requirements

Effective Requirements Writing – Avoiding Ambiguous Requirements

Effective Requirements Writing – Avoiding Ambiguous Requirements

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Effective requirements writing is crucial in the automotive industry, particularly for car manufacturers, where safety is a top priority. The requirements are a critical component of any project and can determine its success or failure. Requirements writing involves specifying the desired behavior of a system, software, or product, and these specifications must be precise, unambiguous, and consistent. Ambiguous requirements can lead to confusion, errors, and potentially hazardous situations. Therefore, it’s essential to avoid ambiguity when writing requirements for ISO 26262, which is a functional safety standard for road vehicles.

ISO 26262 and Safety Requirements

ISO 26262 provides a framework for developing safety-related systems for the automotive industry. It outlines the safety requirements for each phase of the product life cycle, from concept to disposal. The standard guides how to identify, analyze, and mitigate safety risks in automotive systems. It also defines the safety goals and safety requirements for each safety function of the system. Thus, ISO 26262 is crucial in ensuring the safety of road vehicles and their passengers.

Risks of Ambiguous Requirements

Ambiguous requirements can undermine the safety of the system and potentially cause accidents. When requirements are ambiguous, they may be open to multiple interpretations. This can lead to errors in design, development, testing, and deployment. For example, if the requirements for the braking system of a car are ambiguous, it can result in a poorly designed brake system that fails to perform its intended function, resulting in accidents. In ISO 26262, ambiguity in requirements is particularly concerning because it can lead to hazardous situations. The standard requires that safety requirements be unambiguous, verifiable, and traceable. Ambiguity in safety requirements can lead to situations in which safety goals are not met, and the safety of the vehicle is compromised.

Best Practices for Writing Unambiguous Requirements

To ensure unambiguous requirements, car manufacturers should follow best practices when writing requirements. These practices include:

  1. Use Clear and Concise Language: When writing requirements, use simple and unambiguous language to express the requirements. Avoid using complex words or phrases that may have multiple interpretations. Clear language will ensure that everyone involved in the project can understand the requirements.
  2. Define Terms and Abbreviations: Define terms and abbreviations used in the requirements to avoid confusion and misinterpretation. If there are any terms or abbreviations used in the requirements that may be unclear, they should be defined in the requirements document. This will ensure that everyone involved in the project understands the meaning of the terms and abbreviations used.
  3. Use Quantifiable and Verifiable Criteria: Use quantifiable and verifiable criteria to define the requirements. For example, use values, tolerances, ranges, and other measurable parameters to define the requirements. Quantifiable criteria will ensure that the requirements can be tested and verified.
  4. Avoid Subjective Terms: Avoid using subjective terms such as “reasonable,” “adequate,” or “sufficient,” as these can be interpreted differently by different people. Instead, use objective terms that are measurable and can be verified.
  5. Avoid Adverbs, Weak Words, and A/B Constructs: Adverbs, weak words, and A/B constructs can make requirements ambiguous. Avoid using words such as “usually,” “sometimes,” or “often,” as they can be open to interpretation. Instead, use words that provide clear direction, such as “must,” “shall,” or “will.”
  6. Avoid Using Multiple Requirements in a Single Statement: This can lead to confusion and make it difficult to verify that all requirements have been met. Each requirement should be expressed in a separate statement.
  7. Use Examples: Use examples to clarify requirements and show how each requirement should be implemented. It is always a good idea to have other experts review your requirements and provide feedback. This can help identify areas of ambiguity or misunderstanding and improve the clarity of the requirements. Peer reviews can be conducted in different ways, such as one-on-one discussions or group reviews. The important thing is to have a fresh set of eyes to review the requirements and offer constructive criticism.
It is also helpful to have a clear and defined process for reviewing requirements. For example, you can set up a checklist of items to review during the peer review process, such as:
  1. Is the language clear and concise?
  2. Are terms and abbreviations defined?
  3. Are requirements quantifiable and verifiable?
  4. Are subjective terms avoided?
  5. Are adverbs, weak words, and A/B constructs avoided?
  6. Are multiple requirements avoided in a single statement?
  7. Are examples used to clarify requirements?
Having a clear process and checklist can help ensure that all requirements are reviewed thoroughly and consistently.

EARS Requirements Approach

One approach that can help in writing effective requirements is the EARS (Essential, Accurate, Relevant, and Specific) approach. The EARS approach emphasizes the importance of writing requirements that are:
  1. Essential: Only include requirements that are necessary for the system or product to function as intended.
  2. Accurate: Ensure that requirements are accurate and reflect the needs of all stakeholders.
  3. Relevant: Write requirements that are relevant to the product or system being developed.
  4. Specific: Write requirements that are specific and unambiguous.
By using the EARS approach, you can focus on writing requirements that are necessary, accurate, relevant, and specific, which can help avoid ambiguity and ensure that the requirements are met.

Importance of Effective Requirements Writing

Writing unambiguous requirements is essential for ensuring the safety and reliability of road vehicles. Ambiguous requirements can lead to confusion, errors, and potentially hazardous situations, especially in the context of functional safety standards like ISO 26262. To avoid ambiguity in requirements, it is important to use clear and concise language, define terms and abbreviations, and use quantifiable and verifiable criteria. Avoid subjective terms, adverbs, weak words, A/B constructs, and the use of multiple requirements in a single statement. Also, whenever possible, use examples and seek peer feedback. Additionally, using a requirements approach like EARS can help ensure that the requirements are essential, accurate, relevant, and specific. By following these best practices and approaches, car manufacturers can write effective requirements that ensure the safety and reliability of their products, meet regulatory standards, and satisfy customer needs and expectations.

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