dido:99_annexes:annex-b-terms-and-definitions:r:reliability

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dido:99_annexes:annex-b-terms-and-definitions:r:reliability [2026/07/11 11:14] – removed - external edit (Unknown date) 127.0.0.1dido:99_annexes:annex-b-terms-and-definitions:r:reliability [2026/08/06 09:13] (current) – nick_dido
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 +====== Reliability ======
  
 +[[dido:99_annexes:annex-b-terms-and-definitions:start|Go up to Terms and Definitions]]
 +
 +===== Discussion =====
 +
 +Reliability is a [[dido:99_annexes:annex-b-terms-and-definitions:q:quality_characteristic|Quality Characteristic]] concerning the degree to which a subject performs specified functions under specified conditions for a specified period.
 +
 +Reliability can apply to:
 +
 +  * A [[dido:99_annexes:annex-b-terms-and-definitions:c:candidate_solution|Candidate Solution]]
 +  * A [[dido:99_annexes:annex-b-terms-and-definitions:d:distributed_system|Distributed System]]
 +  * A [[dido:99_annexes:annex-b-terms-and-definitions:n:node|Node]]
 +  * A Qualified Node
 +  * A [[dido:99_annexes:annex-b-terms-and-definitions:n:node_set|Node Set]]
 +  * A service
 +  * A software component
 +  * A hardware component
 +  * An [[dido:99_annexes:annex-b-terms-and-definitions:e:execution_facility|Execution Facility]]
 +  * An [[dido:99_annexes:annex-b-terms-and-definitions:o:operational_resource|Operational Resource]]
 +  * Another subject required to perform specified functions
 +
 +Reliability does not mean that a subject never fails. Reliability concerns whether the subject satisfies defined expectations for operation under stated conditions for a stated period.
 +
 +Reliability can concern:
 +
 +  * Availability
 +  * Continuity of operation
 +  * Failure frequency
 +  * Failure rate
 +  * Fault tolerance
 +  * Degraded operation
 +  * Recovery
 +  * State preservation
 +  * Information preservation
 +  * Evidence continuity
 +  * Successful completion
 +  * Service-level behavior
 +  * Another reliability-related property
 +
 +Reliability can identify:
 +
 +  * The evaluated subject
 +  * The specified functions
 +  * The specified operating conditions
 +  * The evaluation period
 +  * The applicable workload
 +  * The applicable [[dido:99_annexes:annex-b-terms-and-definitions:t:test_environment|Test Environment]]
 +  * The applicable [[dido:99_annexes:annex-b-terms-and-definitions:c:configuration|Configuration]]
 +  * The applicable failure conditions
 +  * The applicable fault conditions
 +  * The applicable failure classifications
 +  * The applicable Reliability measures
 +  * The applicable measurement units
 +  * The required measurement precision
 +  * The permitted tolerance
 +  * The applicable DIDO [[dido:99_annexes:annex-b-terms-and-definitions:b:baseline|Baseline]]
 +  * The applicable [[dido:99_annexes:annex-b-terms-and-definitions:v:validation_criteria|Validation Criteria]]
 +  * The applicable [[dido:99_annexes:annex-b-terms-and-definitions:a:acceptance_criteria|Acceptance Criteria]]
 +  * Its [[dido:99_annexes:annex-b-terms-and-definitions:e:evidence|Evidence]]
 +  * Its [[dido:99_annexes:annex-b-terms-and-definitions:p:provenance|Provenance]]
 +  * Its [[dido:99_annexes:annex-b-terms-and-definitions:t:traceability|Traceability]]
 +
 +Reliability can be evaluated using measures such as:
 +
 +  * Successful operations per attempted operation
 +  * Successful [[dido:99_annexes:annex-b-terms-and-definitions:t:test_run|Test Runs]] per attempted Test Run
 +  * Failures per unit of time
 +  * Failures per number of operations
 +  * Mean time between failures
 +  * Mean time to failure
 +  * Availability during the evaluation period
 +  * Successful recovery attempts per recovery attempt
 +  * Information or state preserved after a failure
 +  * Evidence continuity after a failure or restart
 +  * Another measure established by the Acceptance Criteria
 +
 +Within the Governed Node Service Market, Reliability supports:
 +
 +  * Trust in repeated governed work
 +  * Service continuity
 +  * Evidence continuity
 +  * Provider comparison
 +  * Competitive Substitution
 +
 +A Qualified Node demonstrates Reliability by performing its governed functions according to the applicable conditions, service expectations, Governance Policies, and Acceptance Criteria.
 +
 +===== Definition =====
 +
 +//[[dido:99_annexes:annex-b-terms-and-definitions:q:quality_characteristic|Quality Characteristic]] concerning the degree to which a subject performs specified functions under specified conditions for a specified period//
 +
 +===== Source =====
 +
 +Adapted from:
 +
 +  * [[https://www.iso.org/standard/78176.html|ISO/IEC 25010:2023, Systems and software Quality Requirements and Evaluation (SQuaRE) — Product quality model]]
 +  * [[https://www.iso.org/standard/35747.html|ISO/IEC 25023:2016, Systems and software Quality Requirements and Evaluation (SQuaRE) — Measurement of system and software product quality]]
 +  * Financial Systems Archetype, Part 7: Governed Node Service Market
 +  * [[dido:99_annexes:annex-b-terms-and-definitions:q:quality_characteristic|Quality Characteristic]]
 +  * DIDO Reference Implementation Conceptual Model
 +  * DIDO-TE draft Requirements Register
 +
 +The original shared definition described Reliability as the ability of a Qualified Node to perform a governed function correctly and consistently under stated operating conditions.
 +
 +This revision generalizes Reliability for use throughout the shared DIDO corpus while preserving the original Qualified Node and Governed Node Service Market application.
 +
 +===== Note =====
 +
 +Reliability differs from [[dido:99_annexes:annex-b-terms-and-definitions:a:availability|Availability]]:
 +
 +  * Availability concerns whether a subject is operational and accessible when required
 +  * Reliability concerns whether a subject performs specified functions under specified conditions for a specified period
 +
 +Availability can contribute to a Reliability evaluation, but Availability and Reliability are not interchangeable.
 +
 +Reliability differs from [[dido:99_annexes:annex-b-terms-and-definitions:f:functional_correctness|Functional Correctness]]:
 +
 +  * Reliability concerns sustained performance of specified functions
 +  * Functional Correctness concerns whether produced results are correct with the required precision
 +
 +A subject can perform an incorrect function consistently.
 +
 +A subject can produce correct results during successful operations while failing too frequently to satisfy its Reliability criteria.
 +
 +Reliability differs from [[dido:99_annexes:annex-b-terms-and-definitions:o:operational_stability|Operational Stability]]:
 +
 +  * Reliability concerns performance of specified functions over a specified period
 +  * Operational Stability concerns whether selected operational characteristics remain within permitted variation
 +
 +Reliability differs from Recoverability:
 +
 +  * Reliability concerns performance under specified conditions for a specified period
 +  * Recoverability concerns restoration of an affected state and required information after an interruption or failure
 +
 +Recoverability can contribute to Reliability but does not replace Reliability.
 +
 +A completed Test Run assigned a failing [[dido:99_annexes:annex-b-terms-and-definitions:v:verdict|Verdict]] does not necessarily indicate a Reliability failure. The Verdict can concern Functional Correctness, Performance Efficiency, Security, Interoperability, or another Evaluation Characteristic.
 +
 +A [[dido:99_annexes:annex-b-terms-and-definitions:t:test_execution_exception|Test Execution Exception]] does not necessarily indicate failure of the evaluated subject. The exception can originate in:
 +
 +  * [[dido:99_annexes:annex-b-terms-and-definitions:d:dido-te|DIDO-TE]]
 +  * The Test Environment
 +  * An Execution Facility
 +  * An Operational Resource
 +  * An external system
 +  * Another supporting subject
 +
 +The applicable Acceptance Criteria should distinguish:
 +
 +  * Failure of the evaluated subject
 +  * Failure of DIDO-TE
 +  * Failure of the Test Environment
 +  * Failure of a supporting Operational Resource
 +  * A Test Execution Exception unrelated to the evaluated subject
 +
 +===== Example =====
 +
 +A persistence Node records Evidence references and retention metadata during normal operating conditions and after a controlled restart.
 +
 +The applicable Acceptance Criteria establish:
 +
 +  * The specified persistence functions
 +  * The operating conditions
 +  * The evaluation period
 +  * The permitted failure frequency
 +  * The required availability
 +  * The required recovery behavior
 +  * The information and Evidence that must remain intact
 +  * The permitted recovery duration
 +
 +The Node exhibits Reliability when it performs the specified functions according to those conditions and limits throughout the evaluation period.
 +
 +In a separate DIDO-TE evaluation, three Candidate Solutions perform the same function for 72 hours under a common workload. DIDO-TE records each attempted operation, successful operation, failure, period of unavailability, recovery attempt, Test Execution Exception, and supporting Evidence.
 +
 +The resulting Test Results support a comparative evaluation of Candidate Solution Reliability.
 +
 +----
 +
 +<WRAP centeralign>
 +© 2026 Dido Solutions, Inc. and Jackrabbit Consulting, Inc.
 +</WRAP>