Measurement:Canonical Units

• 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 machine-readable physical 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.

Currencies are not represented as UCUM units in AOWIS. Monetary values use currencies identified by ISO 4217 and follow the monetary-value rules defined on this page.

General Rules

• All physical unit identifiers MUST conform to UCUM.
• Each fixed or resolved physical 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.
• A numeric value is not necessarily a measurement quantity. Counts, indices, priorities, precision values, identifiers, and similar non-measurement numbers do not receive UCUM unit identifiers merely because they are numeric.
• Dimensionless physical quantities use the UCUM unity unit 1. Fixed-schema fields whose canonical unit is 1 do not require an AOWIS unit suffix when the field name unambiguously identifies the dimensionless quantity.
• A numeric value whose physical quantity depends on another field, enum, object type, equation, or operating mode MUST NOT be assigned a misleading fixed unit. It MUST be resolved through a quantity-specific field or discriminated structure.
• Equation coefficients whose dimensions depend on a configurable non-integer exponent MUST be stored together with the equation parameters that determine their dimensional meaning and MUST NOT be represented as if they had one fixed standalone UCUM unit.
• Backend-native, imported, display, and user-selected units MUST be converted to the canonical AOWIS representation at system boundaries unless the backend-native representation is itself the canonical AOWIS representation.
• Currencies and exchange rates are outside UCUM unit conversion. Monetary values MUST identify or reference their ISO 4217 currency.

Requirements

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

REQ-MEAS-UNI-002: Each fixed or resolved physical 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.

REQ-MEAS-UNI-005: Dimensionless physical measurement quantities MUST use the UCUM unit identifier "1". A fixed-schema field with canonical unit "1" MAY omit a unit suffix when its field name unambiguously identifies the quantity.

REQ-MEAS-UNI-006: Numeric values that are not physical measurement quantities MUST NOT be assigned UCUM unit identifiers solely because they are numeric.

REQ-MEAS-UNI-007: A value whose physical quantity depends on another field, enum, object type, equation, or operating mode MUST be represented using quantity-specific fields or a discriminated structure that identifies the resolved quantity.

REQ-MEAS-UNI-008: An equation coefficient whose dimensions depend on a configurable non-integer exponent MUST be stored together with the parameters that determine its dimensional meaning and MUST NOT be assigned a misleading fixed standalone UCUM unit.

REQ-MEAS-UNI-009: Non-canonical backend, import, display, or user-selected units MUST be converted to the canonical AOWIS representation at system boundaries.

REQ-MEAS-UNI-010: Currencies MUST NOT be represented as UCUM units in AOWIS. Monetary values MUST identify or reference a currency using its ISO 4217 currency identifier.

Interpretation of the Requirements

This section is informative. The normative requirements above remain authoritative.

The requirements distinguish physical measurement quantities from other numeric values and from monetary values. Physical measurement quantities use canonical UCUM units, including UCUM 1 for dimensionless physical quantities. Numeric values such as counts, priorities, indices, or precision settings are not measurement quantities merely because they are numeric and therefore do not require UCUM units.

A measurement value whose physical quantity depends on another field, object type, operating mode, or equation must first be resolved to a specific measurement quantity. Once resolved, that quantity uses the canonical UCUM unit defined by AOWIS. This applies, for example, to valve settings, control and rule values, water-quality values, report thresholds, and similar context-dependent fields.

Backend, import, export, user-selected, and display units do not change the canonical AOWIS representation. Conversion to and from non-canonical units occurs at system boundaries.

Equation coefficients whose dimensions depend on configurable parameters, such as an arbitrary emitter exponent, must retain the parameters required to interpret their dimensional meaning and must not be assigned a misleading fixed unit.

Monetary values are outside the UCUM measurement-unit system. Their currency is identified or referenced using ISO 4217, while any physical denominator such as kilowatt-hour or kilowatt remains governed by this measurement standard.

Examples

Example	Interpretation
volumetric_flow_rate = 12.5 m3/h	Physical measurement; canonical UCUM unit m3/h
demand_multiplier = 1.2	Dimensionless physical measurement; canonical UCUM unit 1
rule_priority = 5	Numeric value, not a physical measurement; no UCUM unit
energy_price = 0.25 EUR/kWh	EUR is ISO 4217 currency information; kW.h is the physical unit in the denominator
FCV setting = 20 m3/h; PRV setting = 30 m	Both are settings, but they resolve to different measurement quantities and therefore different canonical units

Canonical Measurement Quantities and Units

The canonical UCUM unit identifier assigned to a measurement quantity is authoritative whenever a unit identifier is represented in serialization or 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. A quantity-specific semantic qualifier MAY be included where a literal unit-only suffix would be ambiguous or misleading; for example, mm2_per_m_head makes explicit that the denominator represents pressure head.

For fixed-schema measurement fields, the measurement quantity and canonical unit MAY be defined normatively by the schema and represented through the field name and its AOWIS identifier suffix. Such fields do not require a separate unit-identifier property.

Dimensionless fixed-schema fields whose canonical unit is 1 normally omit a unit suffix. Semantic words such as ratio, factor, coefficient, multiplier, and exponent describe the quantity and are not unit suffixes.

When a unit identifier is represented explicitly, it MUST use the canonical UCUM identifier assigned to the measurement quantity. The AOWIS identifier suffix is a technical field-naming convention and is not itself a UCUM unit identifier.

Generic or dynamically typed physical measurement values MUST explicitly identify their resolved measurement quantity and canonical UCUM unit and MUST NOT rely solely on a field-name suffix.

Each identifier suffix is explicitly defined in the following tables.

Length and Distance 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
darcy_weisbach_roughness_height	Absolute pipe-wall roughness height used by the Darcy-Weisbach head-loss formulation	millimetre (mm)	mm	mm	EPANET Darcy-Weisbach pipe roughness

Geographic Coordinate Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
latitude	Angular position north or south of the equator	degree (°)	deg	deg	WGS 84 latitude
longitude	Angular position east or west of the prime meridian	degree (°)	deg	deg	WGS 84 longitude
projected_easting	Eastward coordinate within a projected coordinate reference system	metre (m)	m	m	UTM, UPS, and other projected-coordinate eastings
projected_northing	Northward coordinate within a projected coordinate reference system	metre (m)	m	m	UTM, UPS, and other projected-coordinate northings
local_x	X coordinate within an explicitly defined local engineering coordinate system	metre (m)	m	m	Local engineering coordinates when the local coordinate system is defined in metres
local_y	Y coordinate within an explicitly defined local engineering coordinate system	metre (m)	m	m	Local engineering coordinates when the local coordinate system is defined in metres

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
water_level	Height of a water surface relative to a defined local reference level	metre (m)	m	m	Initial, minimum, maximum, and simulated tank levels
head_gain	Increase in hydraulic head across an energy-adding component	metre (m)	m	m	Pump head curves and pump simulation results
head_loss	Reduction in hydraulic head across a hydraulic component	metre (m)	m	m	Total head loss across pipes, valves, and other energy-dissipating components
head_loss_gradient	Hydraulic head loss per unit pipe length	metre per kilometre (m/km)	m/km	m_per_km	EPANET pipe head-loss reporting
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

Hydraulic Coefficients and Other Dimensionless Quantities

The canonical UCUM unit identifier for the quantities in this section is 1. The AOWIS unit suffix is intentionally omitted. Semantic field-name components such as ratio, factor, coefficient, multiplier, and exponent remain part of the quantity name where useful.

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
hazen_williams_roughness_coefficient	Empirical pipe roughness coefficient used by the Hazen-Williams head-loss formulation	dimensionless	1	none	EPANET Hazen-Williams pipe roughness
chezy_manning_roughness_coefficient	Empirical pipe roughness coefficient used by the Chezy-Manning head-loss formulation	dimensionless	1	none	EPANET Chezy-Manning pipe roughness
minor_loss_coefficient	Dimensionless coefficient representing local hydraulic losses through fittings, valves, or other components	dimensionless	1	none	Pipe and valve minor-loss coefficient; TCV setting
darcy_weisbach_friction_factor	Dimensionless friction factor used in Darcy-Weisbach head-loss calculations	dimensionless	1	none	Pipe simulation friction factor
pump_speed_ratio	Pump rotational speed relative to its nominal or reference speed	dimensionless	1	none	Pump initial speed, simulated speed, pattern-modified speed, and pump control/rule settings
pattern_multiplier	Dimensionless factor applied by a hydraulic or energy pattern	dimensionless	1	none	EPANET pattern factors
demand_multiplier	Global factor applied to base demands	dimensionless	1	none	EPANET demand multiplier
pressure_exponent	Exponent used by the pressure-driven demand relation	dimensionless	1	none	EPANET pressure exponent
emitter_exponent	Exponent used by the emitter pressure-flow relation	dimensionless	1	none	EPANET emitter exponent
reaction_order	Exponent defining the order of a bulk, wall, or tank reaction equation	dimensionless	1	none	EPANET bulk, wall, and tank reaction orders
specific_gravity	Fluid density relative to the reference density used by the hydraulic solver	dimensionless	1	none	EPANET specific gravity
relative_viscosity	Fluid kinematic viscosity relative to the solver's reference viscosity	dimensionless	1	none	EPANET relative viscosity
relative_diffusivity	Molecular diffusivity relative to the solver's reference diffusivity	dimensionless	1	none	EPANET relative diffusivity
mixing_fraction	Fraction of tank volume assigned to the mixing zone in applicable tank mixing models	dimensionless	1	none	EPANET tank mixing fraction
hydraulic_accuracy	Relative convergence criterion used by the hydraulic solver	dimensionless	1	none	EPANET hydraulic accuracy
hydraulic_damping_limit	Relative accuracy threshold at which hydraulic solution damping/status checks are activated	dimensionless	1	none	EPANET damping limit
relative_error	Relative numerical error reported by a solver or conformance check	dimensionless	1	none	Hydraulic simulation statistics
flow_balance_ratio	Ratio of total outflow to total inflow	dimensionless	1	none	EPANET flow-balance reporting
quality_mass_balance_ratio	Ratio expressing conservation of transported water-quality mass	dimensionless	1	none	EPANET water-quality mass-balance statistic

Percentage Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
efficiency	Ratio of useful output to total input, expressed as a percentage	percent (%)	%	percent	Pump efficiency values and efficiency curves
relative_flow	Flow relative to a defined reference flow, expressed as a percentage	percent (%)	%	percent	Valve characteristic curves
valve_position	Valve opening position relative to its full operating range	percent (%)	%	percent	Position-control valves and valve characteristic curves
source_trace_percentage	Proportion of water originating from a specified source node	percent (%)	%	percent	EPANET source-trace analysis
operating_time_percentage	Fraction of a reporting period during which equipment is operating, expressed as a percentage	percent (%)	%	percent	Pump energy reporting time online
demand_reduction_percentage	Reduction in delivered demand relative to requested demand, expressed as a percentage	percent (%)	%	percent	Hydraulic simulation statistics
leakage_loss_percentage	Leakage loss relative to total system inflow, expressed as a percentage	percent (%)	%	percent	EPANET leakage-loss statistic

Reaction and Leakage Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
first_order_bulk_reaction_coefficient	First-order reaction-rate coefficient for a substance within the bulk fluid	per day (d⁻¹)	/d	per_d	Global, pipe-specific, and tank-specific first-order bulk reaction coefficients
first_order_wall_reaction_coefficient	First-order reaction-rate coefficient for a substance at a pipe wall	metre per day (m/d)	m/d	m_per_d	Global and pipe-specific first-order wall reaction coefficients
leak_area_per_100m_pipe_length	Effective leak area assigned per 100 metres of pipe length	square millimetre per 100 metres (mm²/100 m)	mm2/(100.m)	mm2_per_100m	EPANET 2.3 FAVAD leak area; EPANET defines the native value per 100 project length units, so non-metric projects require conversion at the adapter boundary
leak_area_expansion_per_pressure_head	Increase in effective leak area per unit pressure head	square millimetre per metre of pressure head (mm²/m)	mm2/m	mm2_per_m_head	EPANET 2.3 FAVAD leak expansion; non-metric projects require pressure-head conversion at the adapter boundary

Water Quality Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
chemical_concentration	Mass concentration of a chemical substance in water	milligram per litre (mg/L)	mg/L	mg_per_l	EPANET chemical-quality input, reaction limiting concentration, quality-source concentration, and simulation results
chemical_mass_flow_rate	Chemical mass introduced into or transported through the system per unit time	milligram per minute (mg/min)	mg/min	mg_per_min	EPANET mass-booster source strength and reported source mass rate when chemical concentration is canonicalized to mg/L
water_age	Time elapsed since water entered the modelled distribution system	hour (h)	h	h	EPANET water-age analysis

Power, Energy, and Electrical Quantities

Measurement Quantity Identifier	Definition	Canonical Unit	Canonical UCUM Unit Identifier	AOWIS Identifier Suffix	AOWIS Model / EPANET Mapping
power	Rate of energy transfer	kilowatt (kW)	kW	kw	Pump power and electrical power
energy	Work performed or energy transferred	kilowatt-hour (kWh)	kW.h	kw_h	Pump energy consumption and electrical energy
energy_intensity	Energy consumed per unit volume of transported water	kilowatt-hour per cubic metre (kWh/m³)	kW.h/m3	kw_h_per_m3	Pump energy-use reporting; canonical replacement for backend-dependent power-per-flow-unit values
electric_current	Rate of electric charge flow	ampere (A)	A	a	Electrical model
voltage	Electric potential difference	volt (V)	V	v	Electrical model
electrical_resistance	Opposition to electric current flow	ohm (Ω)	Ohm	ohm	Electrical model
capacitance	Ability to store electric charge	farad (F)	F	f	Electrical model

Monetary Values and Currencies

Currencies are identifiers for monetary value and are not physical units in the AOWIS measurement system. AOWIS therefore does not encode currencies or currency compounds as UCUM unit identifiers.

A monetary value MUST identify or reference a currency definition whose identifier is the ISO 4217 alphabetic currency code. The currency definition MAY be managed by the AOWIS Controller or another authoritative subsystem.

AOWIS MAY support multiple currencies simultaneously. Exchange rates, exchange-rate timestamps, conversion policy, rounding policy, and accounting policy belong to the currency/controller subsystem and MUST NOT be treated as physical unit conversions.

Where a monetary quantity is normalized by a physical quantity, the physical denominator MUST use the canonical AOWIS physical unit. This yields the following canonical monetary semantics:

Monetary Quantity Identifier	Definition	Currency Representation	Canonical Physical Denominator	AOWIS Model / EPANET Mapping
energy_price	Monetary price charged per unit of electrical energy	ISO 4217 currency reference	kilowatt-hour (kWh)	Global and pump-specific energy price
demand_charge_rate	Monetary demand charge per unit of peak power	ISO 4217 currency reference	kilowatt (kW)	Global demand charge
daily_cost_rate	Monetary cost accumulated or averaged per day	ISO 4217 currency reference	day (d)	Average pump cost, energy cost, demand charge, and total cost reporting

A monetary value MUST NOT be interpreted without its currency reference. Two monetary values denominated in different currencies MUST NOT be compared, added, or aggregated without an explicit currency conversion performed by the currency/controller subsystem.

Context-Dependent Measurement Values

A numeric field whose measurement quantity or unit depends on another field, enum, object type, equation, or operating mode MUST NOT be assigned a single fixed canonical unit or AOWIS identifier suffix before that context has been resolved.

Such values MUST be represented using quantity-specific fields or a discriminated data structure that identifies the applicable measurement quantity. Once resolved to a defined measurement quantity, the value MUST use that quantity's canonical AOWIS unit.

Current Model Concept	Context-Dependent Meaning	Required Resolution
Valve setting	PRV, PSV, and PBV settings are pressure head; FCV setting is volumetric flow rate; TCV setting is a minor-loss coefficient; PCV setting is valve position; GPV uses a curve reference rather than a numeric physical setting	Replace the generic numeric setting with quantity-specific fields or a discriminated valve-setting structure
Pump setting	Pump speed setting is a pump-speed ratio rather than a flow, head, or percentage	Represent pump settings explicitly as pump_speed_ratio
Control action setting	The setting quantity supported by the controlled link type	Use the same quantity-specific representation as the target link
Control trigger level or pressure	Water level or pressure head, depending on the controlled node and control type	Represent water-level and pressure-head triggers separately
Rule premise value	Demand, hydraulic head, water level, pressure head, volumetric flow rate, power, elapsed time, time of day, fill time, drain time, or another quantity selected by the rule variable	Store the rule variable together with a quantity-specific value representation
Rule action setting	The setting quantity supported by the target link type	Use the same quantity-specific representation as the target link
Initial quality and simulation quality	Chemical concentration, water age, or source-trace percentage, depending on the quality-analysis mode	Represent each quality-analysis value using its defined measurement quantity
Water-quality solver tolerance	Chemical concentration, water age, or source-trace percentage, depending on the quality-analysis mode	Bind the tolerance to the selected quality-analysis mode and represent it using that mode's canonical quantity
Quality-source strength	Chemical concentration or chemical mass flow rate, depending on the quality-source type	Represent source strength using a source-type-specific structure
Reported source mass rate	Chemical mass flow rate in chemical-quality analysis; other quality-analysis modes must not be mislabeled as chemical mass	Resolve the result through the active quality-analysis mode before assigning chemical_mass_flow_rate
Bulk and wall reaction coefficients	The dimensions of the coefficient depend on the configured reaction order	Use first-order fixed quantities only when the reaction order is exactly first order; otherwise store the coefficient together with reaction order in a discriminated reaction-coefficient structure
Roughness-correlation reaction parameter	The parameter belongs to the configured wall-reaction correlation model and does not have a universally valid standalone measurement unit	Store it as part of the applicable reaction model rather than assigning a guessed fixed unit
Emitter coefficient	In the canonical AOWIS emitter equation Q = C H^n, Q is volumetric flow rate in m³/h, H is pressure head in m, and n is the dimensionless emitter exponent; the dimensional meaning of C therefore depends on n	Store the coefficient and exponent together in a dedicated emitter relation. The coefficient MUST NOT claim one fixed standalone UCUM unit for arbitrary non-integer n
Generic curve coordinates	Coordinate quantities determined by the curve type	Use a typed curve structure whenever the coordinate quantities are known; only genuinely generic curves may carry explicit quantity metadata
Report thresholds	The measurement quantity of the corresponding report field	Associate each threshold with the report field's defined measurement quantity and canonical unit
EPANET map and backdrop coordinates	Coordinate units determined by the associated EPANET map or backdrop configuration; None does not define a physical unit	Convert to an explicitly identified geographic, projected, or local coordinate representation before treating the coordinates as physical measurements

Boundary Conversion Rules

AOWIS canonical units define the public data contract. Backend-selected unit systems MUST NOT leak into fixed-schema AOWIS measurement fields.

The EPANET adapter MUST convert EPANET values to and from the canonical AOWIS units whenever EPANET's selected unit system differs from the canonical AOWIS representation.

This includes, where applicable:

• volumetric flow rates to and from m3/h;
• lengths and hydraulic heads to and from m;
• link diameters to and from mm;
• tank diameters to and from m;
• Darcy-Weisbach roughness to and from mm;
• head-loss gradients to and from m/km;
• leakage area to and from mm2/(100.m);
• leakage expansion to and from mm2/m of pressure head;
• energy-use reporting to kW.h/m3 where the backend reports power per selected flow unit;
• chemical concentration to mg/L when chemical-quality support is active;
• chemical mass flow rate to mg/min when chemical-quality support is active.

A backend configuration value that selects how the backend displays or interprets units is not itself a substitute for unit information in the AOWIS data contract.

Data Model

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

Fixed-schema fields encode their canonical unit through the normative schema and, where applicable, the AOWIS identifier suffix. Dimensionless fixed-schema fields with UCUM unit 1 may omit a unit suffix when their quantity is unambiguous. Generic or dynamically typed physical measurement values carry or resolve to an explicit canonical UCUM unit identifier.

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

Monetary fields defined by the model MUST identify or reference an ISO 4217 currency and MUST follow the monetary-value rules on this page.