Measurement:Unit Identifiers

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

AOWIS uses the canonical SI-based engineering units specified in Units. UCUM is the normative syntax and code system for the 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 unit 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

The canonical UCUM unit identifier is authoritative for serialization and data exchange.

The AOWIS identifier suffix is an ASCII-safe representation used in field names, property names, database columns, and other technical identifiers. Division is represented by _per_, multiplication by _, and upper case is normalized to lower case.

Each identifier suffix is explicitly defined in the following tables.

Length and Spatial Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
length	Linear spatial extent along an object or path	metre (m)	m	m	Pipe and link length
elevation	Vertical height relative to an engineering or hydraulic datum	metre (m)	m	m	Junction, tank, reservoir, and terrain elevation
altitude	Vertical position reported by a geographic positioning source	metre (m)	m	m	Geographic altitude; not necessarily suitable as hydraulic elevation
distance	Spatial separation between positions	metre (m)	m	m	Derived geometric distance
vertical_offset	Vertical difference between referenced elevations or heads	metre (m)	m	m	Elevation, tank-bottom, and reservoir-head offsets
link_diameter	Internal or nominal diameter of a pipe or valve	millimetre (mm)	mm	mm	EPANET pipe and valve diameter
tank_diameter	Internal diameter of a cylindrical storage tank	metre (m)	m	m	EPANET tank diameter

Area and Volume

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
area	Two-dimensional spatial extent	square metre (m²)	m2	m2	Tank cross-sectional area and other geometric areas
volume	Three-dimensional spatial extent or storage capacity	cubic metre (m³)	m3	m3	Tank volume

Flow and Transport

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
volumetric_flow_rate	Volume transported per unit time	cubic metre per hour (m³/h)	m3/h	m3_per_h	Demand, link flow, leakage flow, emitter flow, and pump-curve flow
velocity	Rate of linear movement	metre per second (m/s)	m/s	m_per_s	Link flow velocity

Hydraulic Head, Pressure, and Stress

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
hydraulic_head	Total mechanical energy per unit weight of fluid expressed as an equivalent fluid-column height	metre (m)	m	m	Junction, reservoir, and tank hydraulic head
pressure_head	Fluid pressure expressed as an equivalent fluid-column height	metre (m)	m	m	EPANET node pressure, pressure-driven demand thresholds, and pressure-control valve settings
pressure	Normal force per unit area within a fluid system	kilopascal (kPa)	kPa	kpa	Physical pressure measurements, sensors, SCADA data, and external-system exchange
stress	Internal force per unit area within a material	megapascal (MPa)	MPa	mpa	Structural and material analysis; not currently represented in the hydraulic model

Time

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
elapsed_time	Time elapsed from a defined simulation or process origin	second (s)	s	s	Simulation elapsed time and time-based control triggers
duration	Length of a time interval	second (s)	s	s	Simulation duration, hydraulic timesteps, quality timesteps, reporting intervals, and rule intervals
time_of_day	Time elapsed since the start of the current day	second (s)	s	s	Simulation start time of day and clock-time controls

Electrical Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix
electric_current	Rate of electric charge flow	ampere (A)	A	a
voltage	Electric potential difference	volt (V)	V	v
electrical_resistance	Opposition to electric current flow	ohm (Ω)	Ohm	ohm
power	Rate of energy transfer	kilowatt (kW)	kW	kw
energy	Work performed or energy transferred	kilowatt-hour (kWh)	kW.h	kw_h
capacitance	Ability to store electric charge	farad (F)	F	f

Data Model

Concrete AOWIS data structures and field definitions are specified by the AOWIS Server Model.

Measurement fields defined by the model MUST use the canonical units specified on this page.