Measurement:Units

• 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).

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.