Measurement:Unit Identifiers

Unit Representation Model

AOWIS defines a canonical set of unit identifiers used in all system interfaces, storage formats, APIs, and inter-system data exchanges.

All unit identifiers MUST be ASCII-only strings and MUST NOT contain Unicode characters, superscripts, or typographic symbols.

Units are machine-readable tokens and are not intended to represent typographic or human-rendered SI notation.

General Rules

All unit identifiers MUST be ASCII-only.
Unit identifiers MUST be unambiguous and consistent across all AOWIS-compliant systems.
Each physical quantity MUST map to exactly one canonical unit.
Units MUST NOT be context-dependent or system-dependent.
Units MUST be stable identifiers suitable for JSON, databases, and file formats.

Canonical Unit Identifiers

Length and Spatial Quantities

length → m
elevation → m
distance → m
position_offset → m

Area and Volume

area → m2
volume → m3

Flow and Transport

volumetric_flow_rate → m3_s
mass_flow_rate → kg_s

Pressure and Stress

pressure → Pa
stress → Pa

Mass and Force

mass → kg
force → N

Time

time → s
duration → s

Electrical Quantities (if applicable)

current → A
voltage → V
resistance → ohm

Quantity vs Unit Semantics

The same unit MAY be used for multiple physical quantities where physically appropriate.

For example:

time and duration both use unit "s"

This does NOT imply equivalence of meaning, only equivalence of unit representation.

Semantic meaning is defined by the quantity field, not the unit identifier.

Data Representation Format

All AOWIS measurement values MUST use the following structure:

{
  "quantity": "<physical_quantity>",
  "value": <numeric_value>,
  "unit": "<canonical_unit>"
}

Example:

{
  "quantity": "pipe_length",
  "value": 1200,
  "unit": "m"
}

Requirements

REQ-MEAS-UNI-001: Unit identifiers MUST be ASCII-only strings.

REQ-MEAS-UNI-002: Unit identifiers MUST NOT contain Unicode characters, superscripts, or typographic symbols.

REQ-MEAS-UNI-003: Each physical quantity in AOWIS MUST map to exactly one canonical unit identifier.

REQ-MEAS-UNI-004: Units MUST be used consistently across all AOWIS system interfaces and storage formats.

REQ-MEAS-UNI-005: Units MUST NOT be context-dependent or implementation-defined.

REQ-MEAS-UNI-006: Semantic meaning MUST be derived from the quantity field, not from the unit identifier.