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 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.

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.

Canonical Unit Identifiers

Length and Spatial Quantities

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

Area and Volume

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

Flow and Transport

Quantity	Definition	Canonical Unit	EPANET Mapping
volumetric_flow_rate	Volume per unit time	m3_s	Link flow (SI-normalized EPANET model)
mass_flow_rate	Mass per unit time	kg_s	Not directly represented (derived)

Pressure and Stress

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

Time

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

Electrical Quantities

Quantity	Definition	Canonical Unit
current	Rate of electric charge flow	A
voltage	Electric potential difference	V
resistance	Opposition to electric current flow	ohm
power	Rate of energy transfer	W	Not represented
energy	Work or transferred electrical energy	J
capacitance	Ability to store electric charge	F

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"
}