Measurement:Unit Identifiers

• Part of: Measurement:Main_Page
• Related to: Measurement:Units

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 lower-case 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 lower-case 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.

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.

REQ-MEAS-UNI-007: The "Quantity / Name" field MUST be the canonical machine-readable identifier for a physical quantity and MUST be used as the key in all AOWIS data formats, APIs, databases, and serialized representations.

REQ-MEAS-UNI-008: The "Quantity / Name" field MUST be treated as an immutable identifier and MUST NOT be modified, localized, abbreviated, or reinterpreted across implementations.

REQ-MEAS-UNI-009: Physical quantity semantics MUST be derived exclusively from the "Quantity / Name" field and MUST NOT be inferred from unit identifiers.

Canonical Unit Identifiers

Length and Spatial Quantities

Quantity / Name	Definition	Canonical Unit (SI symbol)	Serialized Unit	EPANET Mapping
length	Linear spatial extent	m	m	Pipe/link length (SI-normalized EPANET model)
elevation	Vertical height relative to datum	m	m	Node elevation (SI-normalized EPANET model)
distance	Spatial separation between points	m	m	Derived geometric quantity
position_offset	Relative spatial offset magnitude	m	m	Not explicitly represented in EPANET

Area and Volume

Quantity / Name	Definition	Canonical Unit (SI symbol)	Serialized Unit	EPANET Mapping
area	Two-dimensional spatial extent	m²	m2	Not directly used
volume	Storage volume	m³	m3	Tank volume (SI-normalized EPANET model)

Flow and Transport

Quantity / Name	Definition	Canonical Unit (SI symbol)	Serialized Unit	EPANET Mapping
volumetric_flow_rate	Volume per unit time	m³/s	m3_s	Link flow (SI-normalized EPANET model)
mass_flow_rate	Mass per unit time	kg/s	kg_s	Not directly represented (derived)

Pressure and Stress

Quantity / Name	Definition	Canonical Unit (SI symbol)	Serialized Unit	EPANET Mapping
pressure	Force per unit area in fluid system	Pa	pa	Node pressure (SI-normalized EPANET model)
stress	Internal material stress	Pa	pa	Not represented

Time

Quantity / Name	Definition	Canonical Unit (SI symbol)	Serialized Unit	EPANET Mapping
time	Simulation or observation time	s	s	Simulation time (EPANET internal time normalized to seconds)
duration	Time interval length	s	s	Simulation duration / reporting intervals

Electrical Quantities

Quantity / Name	Definition	Canonical Unit (SI symbol)	Serialized Unit
current	Rate of electric charge flow	A	a
voltage	Electric potential difference	V	v
resistance	Opposition to electric current flow	Ω	ohm
power	Rate of energy transfer	W	w
energy	Work or transferred electrical energy	J	j
capacitance	Ability to store electric charge	F	f

Data Representation Format

All AOWIS measurement values MUST use the following structure:

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

Example:

{
  "quantity": "pipe_length",
  "value": 1200,
  "unit": "m",
  "uncertainty": 5
}