Functional Correctness

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Functional Correctness is a Quality Characteristic concerning the degree to which a subject produces correct results with the required precision.

Functional Correctness can apply to:

• A Candidate Solution
• A Distributed System
• A Node
• A Node Set
• A service
• A software component
• A calculation
• A transformation
• A transaction
• A decision
• Another subject producing an observable result

Functional Correctness can concern:

• Calculated values
• Generated values
• Transformed values
• Selected values
• Stored values
• Transmitted values
• State transitions
• Transaction outcomes
• Decisions
• Messages
• Events
• Other functional outputs

Functional Correctness can identify:

• The evaluated function
• The applicable inputs
• The applicable Test Argument Values
• The applicable Expected Results
• The observed Test Results
• The required precision
• The permitted tolerance
• The comparison method
• The reference value
• The applicable DIDO Baseline
• The applicable Validation Criteria
• The applicable Acceptance Criteria
• Its Evidence
• Its Provenance
• Its Traceability

Functional Correctness can be evaluated by comparing an observed Test Result with:

• An Expected Result
• An authoritative reference value
• A result produced by an approved reference implementation
• A corresponding Test Result in a controlling DIDO Baseline
• A result calculated using an independently verified method
• Another reference established by the Acceptance Criteria

Quality Characteristic concerning the degree to which a subject produces correct results with the required precision

Adapted from:

• ISO/IEC 25010:2023, Systems and software Quality Requirements and Evaluation (SQuaRE) — Product quality model
• Quality Characteristic
• Expected Result
• Test Result
• DIDO Reference Implementation Conceptual Model
• DIDO-TE draft Requirements Register

ISO/IEC 25010 identifies Functional Correctness as a product-quality subcharacteristic associated with producing correct results with the required precision.

This definition adapts that concept for DIDO-TE evaluation of Candidate Solutions, Distributed Systems, Nodes, services, components, calculations, transactions, and other subjects producing observable results.

Functional Correctness differs from functional completeness:

• Functional Correctness concerns whether produced results are correct
• Functional completeness concerns whether the available functions cover the specified tasks and objectives

Functional Correctness differs from functional appropriateness:

• Functional Correctness concerns the correctness of results
• Functional appropriateness concerns whether functions facilitate accomplishment of specified tasks and objectives

Functional Correctness differs from Reliability:

• Functional Correctness concerns whether a produced result is correct
• Reliability concerns the degree to which a subject performs specified functions under specified conditions for a specified period

A subject can produce an incorrect result reliably.

A subject can produce correct results during successful operations while experiencing unacceptable failures.

Functional Correctness does not require exact equality when the applicable Acceptance Criteria permit:

• Numerical tolerance
• Statistical tolerance
• Rounding
• Approximation
• Nondeterministic ordering
• Equivalent representations
• Another bounded variation

The applicable Acceptance Criteria determine:

• The authoritative Expected Result or reference value
• The comparison method
• The required precision
• The permitted tolerance
• The treatment of missing values
• The treatment of invalid values
• The treatment of nondeterministic results

A passing Verdict can indicate that an observed Test Result satisfies the Functional Correctness criteria applicable to a particular Test Step or Test Run.

One passing Verdict does not necessarily establish Functional Correctness across every input, condition, Configuration, or operational context.

Three Candidate Solutions calculate the expected settlement amount for the same financial agreement.

The applicable Acceptance Criteria establish:

• The financial agreement
• The applicable calculation rules
• The Test Argument Values
• The authoritative Expected Result
• The currency
• The required decimal precision
• The permitted rounding method
• The permitted tolerance

DIDO-TE performs the applicable Test Definition for each Candidate Solution and compares each resulting Test Result with the authoritative Expected Result.

A Candidate Solution exhibits Functional Correctness for the evaluated calculation when its Test Result satisfies the required precision and permitted tolerance.