Dissimilarity
Section 06: System Safety & Functional Safety
Definition
A design strategy in which redundant elements are implemented using different technologies, different design approaches, different hardware components, different software implementations, or different development teams, to reduce the likelihood that a common design error, manufacturing defect, or systematic failure affects all redundant elements simultaneously. Dissimilarity specifically targets systematic common causes that cannot be addressed by physical separation alone.
Where This Shows Up
Dissimilarity is particularly important for addressing systematic failures — errors that are deterministic and repeatable, as opposed to random hardware failures. If two redundant flight computers run identical software, a software defect could cause both to fail simultaneously. Dissimilar software (different algorithms, different languages, different teams) reduces this risk. Dissimilarity comes at significant cost in development and maintenance, so its application is typically limited to the most safety-critical functions.
Primary Sources
Discusses dissimilarity as an architectural strategy for addressing systematic common causes.
Related Terms
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