AOWIS is based on the International System of Units (SI), as specified in Units. Accordingly, AOWIS uses UCUM[1] 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 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.
