Unit Representation Model
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.
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
|
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"
}
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.
