Measurement:Units: Difference between revisions

Latest revision as of 12:12, 28 July 2026

Part of: Measurement:Main_Page
Related to: Measurement:Unit_Identifiers

AOWIS-compliant systems, components, interfaces, and data models MUST use the canonical set of SI-based engineering units defined for measurement quantities in AOWIS.

SI is the globally accepted standard for scientific and technical measurement and is defined and maintained by the International Bureau of Weights and Measures (BIPM).^[1]^[2]

Canonical units are selected individually for each measurement quantity based on the International System of Units (SI), established engineering practice, numerical practicality, and interoperability.

Purpose

This specification establishes a single authoritative canonical unit for each measurement quantity represented by AOWIS.

The use of canonical units reduces implementation complexity, eliminates ambiguity during data exchange, simplifies validation and testing, and improves interoperability between independent AOWIS implementations.

Each measurement quantity is assigned exactly one canonical unit. Authoritative values within the AOWIS measurement model are represented in that unit.

Values received in supported alternative units are converted at the applicable system boundary. Values MAY be converted to other units for external systems or user-interface presentation without changing their canonical representation.

User interfaces MAY display numerical values in supported alternative units for convenience, provided that the displayed unit is clearly indicated. Such presentation does not change the canonical value used by AOWIS.

Terminology

AOWIS domain model: The authoritative representation of concepts, entities, relationships, and state managed by AOWIS.

AOWIS measurement model: The part of the AOWIS domain model that represents measurement quantities, measurement values, units, precision, timestamps, and measurement provenance.

Canonical value: The authoritative numerical representation of a measurement value expressed in the canonical unit defined for its measurement quantity.

Source value: The original numerical value and unit representation received from a user, device, file, component, or external system before validation and conversion into the canonical AOWIS representation.

Requirements

General

REQ-MEAS-001: All authoritative numerical values representing measurement quantities within the AOWIS measurement model MUST be represented using their defined canonical units.

REQ-MEAS-002: Conversion artifacts, rounding errors, and precision loss introduced by an implementation MUST NOT exceed the documented precision of the measurement.

REQ-MEAS-003: Interfaces between AOWIS-compliant components and components or systems using non-canonical unit representations MUST perform the required conversion at the applicable boundary. Values entering the AOWIS measurement model MUST be converted to their defined canonical units. Values leaving AOWIS MAY be converted to the representation required by the receiving component or system.

REQ-MEAS-004: Original source values and their unit identifiers MAY be retained as provenance data. Retained source values MUST be clearly distinguished from the authoritative canonical values and MUST NOT be used as authoritative values for computation, comparison, validation, or control logic.

REQ-MEAS-005: Each distinct measurement quantity in AOWIS MUST be mapped to exactly one canonical unit. Measurement quantities with different meanings MUST have separate identifiers, even when they use the same canonical unit.

User Interface Specific

REQ-MEAS-UI-001: User interfaces MUST clearly indicate the unit associated with every displayed or entered numerical value representing a physical quantity.

REQ-MEAS-UI-002: User interfaces MAY display measurement values in supported non-canonical units for convenience, provided that the displayed unit is clearly indicated.

REQ-MEAS-UI-003: User interfaces accepting values in non-canonical units MUST convert the entered value to its defined canonical unit before it enters the AOWIS measurement model.

REQ-MEAS-UI-004: Rounding performed for presentation MUST NOT modify the underlying canonical value.

Notes

External systems MAY use alternative unit systems. Any required conversion between such systems and AOWIS is performed at the system boundary in accordance with REQ-MEAS-003.

References

↑ International Bureau of Weights and Measures (BIPM) — International System of Units (SI) https://www.bipm.org/en/measurement-units/si-base-units
↑ NIST — The International System of Units (SI) https://www.nist.gov/pml/owm/metric-si/si-units

[BIPM-SI-1] International Bureau of Weights and Measures (BIPM) — International System of Units (SI) https://www.bipm.org/en/measurement-units/si-base-units

[NIST-SI-2] NIST — The International System of Units (SI) https://www.nist.gov/pml/owm/metric-si/si-units

[1]

[2]

@@ Line 1: / Line 1: @@
-AOWIS systems, components, and data models MUST use the International System of Units (SI) as the canonical unit system.<ref name="BIPM-SI">International Bureau of Weights and Measures (BIPM) — International System of Units (SI) https://www.bipm.org/en/measurement-units/si-base-units</ref><ref name="NIST-SI">NIST — The International System of Units (SI) https://www.nist.gov/pml/owm/metric-si/si-units</ref>
+* Part of: [[Measurement:Main_Page]]
+* Related to: [[Measurement:Unit_Identifiers]]
-SI is the globally accepted standard for scientific and technical measurement and is defined and maintained by the International Bureau of Weights and Measures (BIPM).<ref name="Wikipedia-SI">Wikipedia — International System of Units https://en.wikipedia.org/wiki/International_System_of_Units</ref>
+AOWIS-compliant systems, components, interfaces, and data models MUST use the canonical set of SI-based engineering units defined for measurement quantities in AOWIS.
-Non-SI unit systems MAY be used for user input and display purposes, provided that:
+SI is the globally accepted standard for scientific and technical measurement and is defined and maintained by the International Bureau of Weights and Measures (BIPM).<ref name="BIPM-SI">International Bureau of Weights and Measures (BIPM) — International System of Units (SI) https://www.bipm.org/en/measurement-units/si-base-units</ref><ref name="NIST-SI">NIST — The International System of Units (SI) https://www.nist.gov/pml/owm/metric-si/si-units</ref>
-* All input values MUST be internally converted to SI units for storage and processing
+Canonical units are selected individually for each measurement quantity based on the International System of Units (SI), established engineering practice, numerical practicality, and interoperability.
-* The original input unit MUST be preserved as metadata where applicable
-* The system MUST clearly indicate the unit associated with every displayed value
+== Purpose ==
-* If multiple unit systems are displayed, SI units MUST be clearly identifiable as the primary reference
-* Conversion between unit systems MUST be deterministic and consistent across implementations
+This specification establishes a single authoritative canonical unit for each measurement quantity represented by AOWIS.
-* User interfaces MAY support alternative unit systems (e.g. imperial units), but SI units remain the authoritative representation within AOWIS.
+The use of canonical units reduces implementation complexity, eliminates ambiguity during data exchange, simplifies validation and testing, and improves interoperability between independent AOWIS implementations.
+Each measurement quantity is assigned exactly one canonical unit. Authoritative values within the AOWIS measurement model are represented in that unit.
+Values received in supported alternative units are converted at the applicable system boundary. Values MAY be converted to other units for external systems or user-interface presentation without changing their canonical representation.
+User interfaces MAY display numerical values in supported alternative units for convenience, provided that the displayed unit is clearly indicated. Such presentation does not change the canonical value used by AOWIS.
+== Terminology ==
+; AOWIS domain model
+: The authoritative representation of concepts, entities, relationships, and state managed by AOWIS.
+; AOWIS measurement model
+: The part of the AOWIS domain model that represents measurement quantities, measurement values, units, precision, timestamps, and measurement provenance.
+; Canonical value
+: The authoritative numerical representation of a measurement value expressed in the canonical unit defined for its measurement quantity.
+; Source value
+: The original numerical value and unit representation received from a user, device, file, component, or external system before validation and conversion into the canonical AOWIS representation.
+== Requirements ==
+=== General ===
-=== Requirements ===
 <pre>
-REQ-MEAS-UNIT-010 — All user interfaces MUST display measurement values in SI units as the primary canonical representation.
+REQ-MEAS-001: All authoritative numerical values representing measurement quantities within the AOWIS measurement model MUST be represented using their defined canonical units.
-REQ-MEAS-UNIT-011 — If a user provides input in a non-SI unit (where supported), the system MUST convert the value to SI units for internal processing and display the SI value as the primary result.
+REQ-MEAS-002: Conversion artifacts, rounding errors, and precision loss introduced by an implementation MUST NOT exceed the documented precision of the measurement.
-REQ-MEAS-UNIT-012 — If a non-SI input unit is provided by the user, the system MUST also display the original user-provided value as secondary information, clearly labeled with its unit and explicitly marked as user-provided input (origin data).
+REQ-MEAS-003: Interfaces between AOWIS-compliant components and components or systems using non-canonical unit representations MUST perform the required conversion at the applicable boundary. Values entering the AOWIS measurement model MUST be converted to their defined canonical units. Values leaving AOWIS MAY be converted to the representation required by the receiving component or system.
-REQ-MEAS-UNIT-013 — The SI-converted value MUST be visually and semantically distinguished as the authoritative representation of the measurement.
+REQ-MEAS-004: Original source values and their unit identifiers MAY be retained as provenance data. Retained source values MUST be clearly distinguished from the authoritative canonical values and MUST NOT be used as authoritative values for computation, comparison, validation, or control logic.
-REQ-MEAS-UNIT-014 — The original user-provided value MUST NOT be used for calculations, control decisions, or storage without conversion to SI units.
+REQ-MEAS-005: Each distinct measurement quantity in AOWIS MUST be mapped to exactly one canonical unit. Measurement quantities with different meanings MUST have separate identifiers, even when they use the same canonical unit.
+</pre>
-REQ-MEAS-UNIT-015 — Unit ambiguity MUST NOT exist in any displayed measurement; each displayed value MUST have an explicitly stated unit.
+=== User Interface Specific ===
+<pre>
+REQ-MEAS-UI-001: User interfaces MUST clearly indicate the unit associated with every displayed or entered numerical value representing a physical quantity.
+REQ-MEAS-UI-002: User interfaces MAY display measurement values in supported non-canonical units for convenience, provided that the displayed unit is clearly indicated.
-* REQ-MEAS-UNIT-001 — All stored measurement values MUST use SI units as the canonical representation.
+REQ-MEAS-UI-003: User interfaces accepting values in non-canonical units MUST convert the entered value to its defined canonical unit before it enters the AOWIS measurement model.
-* REQ-MEAS-UNIT-002 — Non-SI input values MUST be converted to SI units before storage or processing.
-* REQ-MEAS-UNIT-003 — The original input unit MUST be preserved as metadata when provided.
+REQ-MEAS-UI-004: Rounding performed for presentation MUST NOT modify the underlying canonical value.
-* REQ-MEAS-UNIT-004 — Systems MUST ensure that every displayed measurement value has an explicitly defined unit.
-* REQ-MEAS-UNIT-005 — SI units MUST be identifiable as the authoritative reference in all multi-unit displays.
-* REQ-MEAS-UNIT-006 — Unit conversions MUST be deterministic and consistent across implementations.
-* REQ-MEAS-UNIT-007 — UI-only display formats MUST NOT affect stored or transmitted canonical SI values.
 </pre>
+== Notes ==
+External systems MAY use alternative unit systems. Any required conversion between such systems and AOWIS is performed at the system boundary in accordance with REQ-MEAS-003.
 == References ==
 <references />

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