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=== Length and Spatial Quantities ===
=== Length and Spatial Quantities ===


* length → m
{| class="wikitable"
* elevation → m
! Quantity !! Definition !! Canonical Unit !! EPANET Mapping
* distance → m
|-
* position_offset → m
| 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 ===
=== Area and Volume ===


* area → m2
{| class="wikitable"
* volume → m3
! 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 ===
=== Flow and Transport ===


* volumetric_flow_rate → m3_s
{| class="wikitable"
* mass_flow_rate → kg_s
! 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 ===
=== Pressure and Stress ===


* pressure → Pa
{| class="wikitable"
* stress → Pa
! Quantity !! Definition !! Canonical Unit !! EPANET Mapping
 
|-
=== Mass and Force ===
| pressure || Force per unit area in fluid system || Pa || Node pressure (SI-normalized EPANET model)
 
|-
* mass → kg
| stress || Internal material stress || Pa || Not represented
* force → N
|}


=== Time ===
=== Time ===


* time → s
{| class="wikitable"
* duration → s
! Quantity !! Definition !! Canonical Unit !! EPANET Mapping
 
|-
=== Electrical Quantities (if applicable) ===
| time || Simulation or observation time || s || Simulation time (EPANET internal time normalized to seconds)
 
|-
* current → A
| duration || Time interval length || s || Simulation duration / reporting intervals
* voltage → V
|}
* resistance → ohm
 
== Quantity vs Unit Semantics ==
 
The same unit MAY be used for multiple physical quantities where physically appropriate.
 
For example:
 
* time and duration both use unit "s"


This does NOT imply equivalence of meaning, only equivalence of unit representation.
=== Electrical Quantities ===


Semantic meaning is defined by the quantity field, not the unit identifier.
{| class="wikitable"
! 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 ==
== Data Representation Format ==

Revision as of 18:38, 10 June 2026

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

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"
}

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.
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