Measurement:Unit Identifiers

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

AOWIS is based on the International System of Units (SI), as specified in Units. Accordingly, AOWIS uses UCUM as the normative syntax and code system for machine-readable unit identifiers.

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

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

General Rules

• All unit identifiers MUST conform to UCUM.
• Each measurement quantity MUST be assigned exactly one UCUM unit identifier as its canonical unit identifier.
• Canonical unit identifiers MUST be used consistently across all AOWIS-compliant systems, interfaces, storage formats, APIs, and inter-system data exchanges.
• Canonical unit identifiers MUST be interpreted independently of locale, display format, implementation, and system context.
• Canonical unit identifiers MUST remain stable across AOWIS-compliant systems and data formats.

Requirements

REQ-MEAS-UNI-001: All unit identifiers MUST conform to UCUM.

REQ-MEAS-UNI-002: Each measurement quantity MUST be assigned exactly one UCUM unit identifier as its canonical unit identifier.

REQ-MEAS-UNI-003: The canonical unit identifier assigned to a measurement quantity MUST be used consistently across all AOWIS-compliant systems, interfaces, storage formats, APIs, and inter-system data exchanges.

REQ-MEAS-UNI-004: The measurement quantity identifier defines what is measured, while the unit identifier defines the unit in which it is expressed.

Canonical Measurement Quantities and Units

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_per_s	Link flow (SI-normalized EPANET model)
mass_flow_rate	Mass per unit time	kg/s	kg_per_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
}