COMET Data Exchange & Transport Layer — Technical Specification

Section 1

COMET as Semantic Middleware

Carbon data today is produced in dozens of proprietary formats across LCA tools, ERP systems, registries, and supplier platforms. Each destination—CBAM declarations, PCF exchanges, carbon credit registries—demands a different schema. COMET resolves this by acting as a semantic middleware layer: a shared namespace that any producer can annotate into and any consumer can query from, without bilateral integration agreements.

The mechanism is JSON-LD @context injection. Any existing payload gains interoperability by referencing the COMET context document. OWL class equivalences allow reasoners to infer alignment across standards automatically.

Data Producers

Supplier Platforms & Tools

Supplier platforms, LCA tools (SimaPro, openLCA), ERP systems, carbon registries. Proprietary formats.

COMET Vocabulary Layer

Shared Namespace

JSON-LD @context injection. Shared namespace. OWL class alignment. SHACL validation.

Data Consumers

Buyers, Regulators & Markets

Industrial buyers, CBAM declarants, carbon verifiers, ESG funds, regulators, carbon markets.

Section 2

WBCSD PACT v3 Integration

WBCSD PACT v3 (Partnership for Carbon Transparency) is the leading interoperability framework for product-level carbon footprints. COMET provides a complete semantic overlay for every PACT v3 field, enabling PACT payloads to be annotated with COMET context and consumed by any COMET-aware system without data transformation.

2a. Field Mapping: ProductFootprint & CarbonFootprint

PACT v3 Field	Type	COMET Class	COMET Property	Notes
id	UUID	comet-pcf:ProductCarbonFootprint	pcfId	Primary identifier
specVersion	String	—	—	Protocol version
version	Integer	—	dcterms:version	Payload version
created	DateTime	—	dcterms:created
updated	DateTime	—	dcterms:modified
status	Enum	—	—	Active/Deprecated
validityPeriodStart	DateTime	comet:TimePeriod	startDate
validityPeriodEnd	DateTime	comet:TimePeriod	endDate
companyName	String	comet:Organization	orgName
companyIds	URN[]	comet:Organization	orgId	LEI, DUNS
productDescription	String	comet:Material	materialName
productIds	URN[]	comet:Material	materialId	GTIN
productCategoryCpc	String	comet:Material	cpcCode	UN CPC
productNameCompany	String	comet:Material	tradeName
pcf.declaredUnit	Enum	comet-pcf:FunctionalUnit	qudtUnit	QUDT binding
pcf.unitaryProductAmount	Decimal	comet-pcf:FunctionalUnit	qudtValue
pcf.pCfExcludingBiogenic	Decimal	comet-pcf:PCF	fossilGWP	kgCO2e/unit
pcf.pCfIncludingBiogenic	Decimal	comet-pcf:PCF	totalGWP
pcf.fossilGhgEmissions	Decimal	comet-pcf:PCF	fossilEmissions
pcf.biogenicCarbonContent	Decimal	comet-pcf:BiogenicCarbon	biogenicCarbonContent
pcf.dLucGhgEmissions	Decimal	comet-pcf:BiogenicCarbon	landUseChange
pcf.biogenicCarbonWithdrawal	Decimal	comet-pcf:BiogenicCarbon	biogenicUptake
pcf.aircraftGhgEmissions	Decimal	comet-sc:TransportEvent	aircraftEmissions
pcf.characterizationFactors	Enum	comet-ef:GWP100Value	ipccAR	AR5/AR6
pcf.crossSectoralStandardsUsed	Enum[]	comet-pcf:StandardRef	standardName
pcf.productOrSectorSpecificRules	Object[]	comet-pcf:PCRReference	pcrName
pcf.boundaryProcessesDescription	String	comet-pcf:SystemBoundary	description
pcf.referencePeriodStart	DateTime	comet:TimePeriod	startDate
pcf.referencePeriodEnd	DateTime	comet:TimePeriod	endDate
pcf.geographyCountry	ISO3166	comet:Site	siteCountry
pcf.geographyRegionOrSubregion	Enum	comet-ef:GeographyScope	region
pcf.exemptedEmissionsPercent	Decimal	comet-pcf:PCF	exemptedPercent
pcf.primaryDataShare	Decimal	comet-sc:PrimaryDataShare	sharePercent	0–100
pcf.dqi.coveragePercent	Decimal	comet-sc:DQI	coverageDQI
pcf.dqi.technologicalDQR	Decimal	comet-sc:DQI	technologyDQI	1–3
pcf.dqi.temporalDQR	Decimal	comet-sc:DQI	temporalityDQI	1–3
pcf.dqi.geographicalDQR	Decimal	comet-sc:DQI	geographyDQI	1–3
pcf.dqi.completenessDQR	Decimal	comet-sc:DQI	reliabilityDQI	1–3
pcf.assurance.assurance	Boolean	comet-ver:AssuranceLevel	hasAssurance
pcf.assurance.level	Enum	comet-ver:AssuranceLevel	levelType	limited/reasonable
pcf.assurance.providerName	String	comet-ver:QualifiedVerifier	verifierName
pcf.assurance.completedAt	DateTime	comet-ver:VerificationClaim	verificationDate
pcf.assurance.standardName	String	comet-ver:VerificationClaim	standardRef
pcf.allocationRulesDescription	String	comet-pcf:AllocationMethod	description
pcf.packagingGhgEmissions	Decimal	comet-pcf:PCF	packagingEmissions

2b. Complete PACT v3 Payload with COMET Context

JSON-LD — PACT v3 Product Carbon Footprint with COMET Context Injection

{
  "@context": [
    "https://wbcsd.github.io/pact/v3/context.json",
    "https://comet.carbon/v1/jsonld/context.json"
  ],
  "@type": "comet-pcf:ProductCarbonFootprint",
  "id": "urn:uuid:b1c4a89e-3c2d-4f5a-b6e7-d8f9a0b1c2d3",
  "specVersion": "3.0.0",
  "version": 1,
  "created": "2025-03-15T10:30:00Z",
  "status": "Active",
  "companyName": "Stahl AG",
  "companyIds": ["urn:lei:5299000J2N45DDNE4Y28"],
  "productDescription": "Hot-rolled steel coil, basic oxygen furnace route",
  "productIds": ["urn:gtin:04012345678901"],
  "productCategoryCpc": "4121",
  "pcf": {
    "declaredUnit": "kilogram",
    "unitaryProductAmount": 1,
    "pCfExcludingBiogenic": 1.85,
    "fossilGhgEmissions": 1.85,
    "biogenicCarbonContent": 0,
    "characterizationFactors": "AR6",
    "crossSectoralStandardsUsed": ["ISO14067"],
    "boundaryProcessesDescription": "Cradle-to-gate: iron ore extraction through hot rolling",
    "referencePeriodStart": "2024-01-01T00:00:00Z",
    "referencePeriodEnd": "2024-12-31T23:59:59Z",
    "geographyCountry": "DE",
    "primaryDataShare": 78.5,
    "dqi": {
      "coveragePercent": 85.0,
      "technologicalDQR": 1.5,
      "temporalDQR": 1.0,
      "geographicalDQR": 1.0,
      "completenessDQR": 2.0
    },
    "assurance": {
      "assurance": true,
      "coverage": "PCF system",
      "level": "limited",
      "providerName": "Bureau Veritas",
      "completedAt": "2025-02-28T00:00:00Z",
      "standardName": "ISO 14064-3"
    }
  }
}

2c. PACT REST API Endpoints

Method	Endpoint	Description	COMET Context
POST	/auth/token	OAuth2 client credentials	Authentication
GET	/2/footprints	List all footprints	Array of comet-pcf:ProductCarbonFootprint
GET	/2/footprints/{id}	Get single footprint	Single comet-pcf:ProductCarbonFootprint
POST	/2/events	Publish events	PF update notifications

Section 3

EU CBAM Declaration Mapping

The EU Carbon Border Adjustment Mechanism (Regulation 2023/956) requires importers to declare embedded emissions for iron, steel, aluminium, cement, fertilisers, electricity, and hydrogen. COMET provides a dedicated comet-pcf:CBAMDeclaration class that maps directly to the CBAM XML schema issued by DG TAXUD, enabling automated declaration generation from structured COMET data.

3a. CBAM Field Mapping

CBAM Field	Regulation Ref	COMET Class	COMET Property	Type
Authorised declarant	Art. 5	comet:Organization	orgId (EORI)	String
CN code	Annex I	comet-pcf:CBAMDeclaration	cnCode	8-digit
Country of origin	Art. 35	comet:Site	siteCountry	ISO 3166
Installation ID	Art. 10	comet:Site	siteId	String
Specific embedded emissions	Art. 7	comet-pcf:EmbeddedEmissions	specificEmbeddedEmissions	tCO2e/t
Direct emissions	Art. 7(2)(a)	comet-pcf:EmbeddedEmissions	directEmissions	tCO2e/t
Indirect emissions	Art. 7(2)(b)	comet-pcf:EmbeddedEmissions	indirectEmissions	tCO2e/t
Production route	Annex IV	comet-pcf:EmbeddedEmissions	productionRoute	String
Carbon price paid	Art. 9	comet-mkt:CBAMShadowTariff	thirdCountryCarbonPrice	EUR
EU ETS benchmark	Art. 31	comet-mkt:MarketBenchmark	benchmarkValue	tCO2e/t
Quantity imported	Art. 35	comet-pcf:FunctionalUnit	qudtValue	tonnes
Reporting period	Art. 35	comet:TimePeriod	startDate/endDate	ISO 8601
Verification	Art. 8, 18	comet-ver:VerificationClaim	—	Object
Precursor emissions	Annex IV	comet-sc:SupplyChainLink	—	Object

3b. CBAM XML with COMET Namespace Annotations

XML — CBAM Declaration with COMET Namespace Annotations

<?xml version="1.0" encoding="UTF-8"?>
<cbam:CBAMDeclaration
  xmlns:cbam="urn:ec:taxud:cbam:v1"
  xmlns:comet="https://comet.carbon/v1/core#"
  xmlns:comet-pcf="https://comet.carbon/v1/pcf#"
  xmlns:comet-mkt="https://comet.carbon/v1/market#"
  xmlns:comet-ver="https://comet.carbon/v1/ver#">

  <cbam:declarant>
    <comet:Organization>
      <comet:orgId type="EORI">DE123456789012345</comet:orgId>
      <comet:orgName>Stahl Import GmbH</comet:orgName>
    </comet:Organization>
  </cbam:declarant>

  <cbam:reportingPeriod>
    <comet:TimePeriod>
      <comet:startDate>2026-01-01</comet:startDate>
      <comet:endDate>2026-03-31</comet:endDate>
    </comet:TimePeriod>
  </cbam:reportingPeriod>

  <cbam:goods>
    <cbam:goodsItem>
      <comet-pcf:CBAMDeclaration>
        <comet-pcf:cnCode>72081000</comet-pcf:cnCode>
        <comet-pcf:embeddedEmissions>
          <comet-pcf:specificEmbeddedEmissions unit="tCO2e/t">1.85</comet-pcf:specificEmbeddedEmissions>
          <comet-pcf:directEmissions unit="tCO2e/t">1.62</comet-pcf:directEmissions>
          <comet-pcf:indirectEmissions unit="tCO2e/t">0.23</comet-pcf:indirectEmissions>
          <comet-pcf:productionRoute>Basic Oxygen Furnace (BOF)</comet-pcf:productionRoute>
        </comet-pcf:embeddedEmissions>
        <comet:Site>
          <comet:siteCountry>TR</comet:siteCountry>
          <comet:siteId>TR-INSTALL-2024-0847</comet:siteId>
        </comet:Site>
        <comet-mkt:CBAMShadowTariff>
          <comet-mkt:euETSPrice currency="EUR">68.50</comet-mkt:euETSPrice>
          <comet-mkt:thirdCountryCarbonPrice currency="EUR">12.00</comet-mkt:thirdCountryCarbonPrice>
        </comet-mkt:CBAMShadowTariff>
        <comet-pcf:FunctionalUnit>
          <comet-pcf:qudtValue>500</comet-pcf:qudtValue>
          <comet-pcf:qudtUnit>tonne</comet-pcf:qudtUnit>
        </comet-pcf:FunctionalUnit>
      </comet-pcf:CBAMDeclaration>
    </cbam:goodsItem>
  </cbam:goods>

  <cbam:verification>
    <comet-ver:VerificationClaim>
      <comet-ver:verifierName>Bureau Veritas</comet-ver:verifierName>
      <comet-ver:assuranceLevel>limited</comet-ver:assuranceLevel>
      <comet-ver:standardRef>ISO 14064-3:2019</comet-ver:standardRef>
    </comet-ver:VerificationClaim>
  </cbam:verification>
</cbam:CBAMDeclaration>

3c. XSD Schema Fragment

XSD — COMET CBAMDeclarationType Schema Fragment

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  xmlns:comet-pcf="https://comet.carbon/v1/pcf#"
  targetNamespace="https://comet.carbon/v1/pcf#">

  <xs:complexType name="CBAMDeclarationType">
    <xs:sequence>
      <xs:element name="cnCode" type="xs:string"/>
      <xs:element name="embeddedEmissions" type="comet-pcf:EmbeddedEmissionsType"/>
      <xs:element name="countryOfOrigin" type="xs:string"/>
      <xs:element name="applicableCarbonPrice" type="xs:decimal" minOccurs="0"/>
    </xs:sequence>
  </xs:complexType>

  <xs:complexType name="EmbeddedEmissionsType">
    <xs:sequence>
      <xs:element name="specificEmbeddedEmissions" type="xs:decimal"/>
      <xs:element name="directEmissions" type="xs:decimal"/>
      <xs:element name="indirectEmissions" type="xs:decimal"/>
      <xs:element name="productionRoute" type="xs:string"/>
    </xs:sequence>
  </xs:complexType>

</xs:schema>

Section 4

CAD Trust Integration

CAD Trust (Climate Action Data Trust) is the interoperability backbone for carbon credit registries, aggregating data from Verra VCS, Gold Standard, ACR, CAR, and others through a unified API. COMET maps all CAD Trust v2.0.2 entities, enabling carbon credit data to flow into COMET-aware procurement, financing, and compliance systems without bilateral registry integrations.

4a. Entity Mapping: CAD Trust v2.0.2

CAD Trust Table	Key API Field	COMET Class	COMET Property	Notes
project	cadTrustProjectId	comet-ver:CADTrustAttestation	cadTrustProjectId	Primary linkage
project	projectRegistryName	comet-eac:CertificateRegistry	registryName
project	projectSector	comet:Process	processType	CDM sectors
unit	unitSerialId	comet-eac:EAC	serialNumber	Credit ID
unit	unitType	comet-eac:EAC	unitType	Avoidance/Reduction/Removal
unit	unitVintageYear	comet-eac:EAC	vintageYear
unit	unitStatus	comet-eac:EAC	unitStatus	Issued/Held/Retired/Cancelled
unit	unitCount	comet-eac:EAC	unitCount
unit	unitRetirementBeneficiary	comet-eac:RetirementEvent	retirementBeneficiary
verification	verificationBody	comet-ver:QualifiedVerifier	verifierName	VVB
validation	validationType	comet-ver:ValidationRecord	validationType
label	labelType	comet-eac:EAC	labelType	Cert/Art.6 types
co_benefit	cobenefit	comet-eac:CoBenefit	sdgGoal	SDG 1–17
rating	ratingType	comet-ver:Rating	ratingProvider	CDP/CCQI
program	programName	comet-eac:CertificateRegistry	programName
estimation	estimationUnitCount	comet-sc:ActivityDataRecord	estimatedQuantity
aef_t2	authorization fields	comet-eac:Article6Authorization	—	Paris Art. 6
aef_t3	transfer fields	comet-eac:Article6Transfer	—	ITMO transfers

4b. Carbon Credit JSON-LD with CAD Trust Attestation

JSON-LD — COMET Carbon Removal Certificate with CAD Trust Attestation

{
  "@context": [
    "https://comet.carbon/v1/jsonld/context.json",
    "https://climateactiondata.org/api/v2/context.json"
  ],
  "@type": "comet-eac:CarbonRemovalCert",
  "comet-eac:serialNumber": "VCS-2847-2024-001-to-500",
  "comet-eac:vintageYear": 2024,
  "comet-eac:unitCount": 500,
  "comet-eac:unitType": "Removal - technical",
  "comet-eac:registry": {
    "@type": "comet-eac:CertificateRegistry",
    "comet-eac:registryName": "Verra VCS",
    "comet-eac:registryURI": "https://registry.verra.org/"
  },
  "comet-ver:CADTrustAttestation": {
    "cadTrustProjectId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
    "cadTrustUnitId": "f0e1d2c3-b4a5-6789-0fed-cba987654321"
  },
  "comet:Site": {
    "comet:siteCountry": "KE",
    "comet:siteRegion": "Rift Valley"
  },
  "comet-ver:VerificationClaim": {
    "comet-ver:verifierName": "DNV",
    "comet-ver:assuranceLevel": "reasonable"
  },
  "comet-eac:CoBenefit": [
    { "sdgGoal": "SDG 13 - Climate action" },
    { "sdgGoal": "SDG 15 - Life on land" }
  ],
  "comet-eac:RetirementEvent": {
    "retirementBeneficiary": "Stahl AG",
    "retirementDate": "2025-06-15"
  }
}

Section 5

GHG Protocol Scope 3 Mapping

The GHG Protocol Corporate Value Chain (Scope 3) Standard defines 15 categories of indirect emissions. COMET classes cover 11 of the 15 categories directly, with the remaining four handled through composition. This table shows the primary COMET class responsible for each category and its expected use case in a corporate carbon accounting workflow.

Cat	Description	COMET Class	Use Case
1	Purchased goods & services	comet-sc:SupplyChainLink + comet-pcf:PCF	Supplier PCF ingestion
2	Capital goods	comet-sc:SupplyChainLink	Asset embodied carbon
3	Fuel & energy activities	comet-ef:EmissionFactor	Well-to-tank factors
4	Upstream transport	comet-sc:TransportEvent	Logistics emissions
5	Waste in operations	comet-pcf:SystemBoundary	End-of-life module
6	Business travel	comet-sc:TransportEvent	Travel emissions
7	Employee commuting	comet-sc:TransportEvent	Commute estimates
9	Downstream transport	comet-sc:TransportEvent	Distribution
11	Use of sold products	comet-pcf:SystemBoundary	Use-phase
12	End-of-life treatment	comet-pcf:SystemBoundary	Disposal/recycling
15	Investments	comet-mkt:CarbonPremium	Financed emissions

Section 6

JSON Schema for COMET PCF

This JSON Schema draft-07 document provides machine-readable validation for COMET ProductCarbonFootprint instances. It can be used directly in API validation pipelines, data quality gates, and SHACL-to-JSON toolchains. The schema enforces required fields, numeric constraints, and controlled vocabulary enumerations aligned with ISO 14067 and PACT v3.

JSON Schema — COMET ProductCarbonFootprint (draft-07)

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$id": "https://comet.carbon/v1/schema/pcf.json",
  "title": "COMET ProductCarbonFootprint",
  "type": "object",
  "required": ["pcfId", "declaredUnit", "fossilGWP", "reportingPeriod", "organization"],
  "properties": {
    "pcfId": { "type": "string", "format": "uuid" },
    "declaredUnit": {
      "type": "string",
      "enum": [
        "kilogram", "liter", "cubic meter",
        "kilowatt hour", "megajoule",
        "tonne kilometre", "square meter"
      ]
    },
    "unitaryProductAmount": { "type": "number", "minimum": 0 },
    "fossilGWP": {
      "type": "number",
      "minimum": 0,
      "description": "kg CO2e per declared unit"
    },
    "totalGWP": { "type": "number" },
    "biogenicCarbon": {
      "type": "object",
      "properties": {
        "biogenicCarbonContent": { "type": "number" },
        "biogenicUptake": { "type": "number" },
        "landUseChange": { "type": "number" },
        "indirectLUC": { "type": "number" }
      }
    },
    "characterizationFactors": { "type": "string", "enum": ["AR5", "AR6"] },
    "systemBoundary": {
      "type": "string",
      "enum": [
        "cradle-to-gate", "gate-to-gate",
        "cradle-to-grave", "cradle-to-cradle"
      ]
    },
    "allocationMethod": {
      "type": "string",
      "enum": [
        "mass", "economic", "energy",
        "physical-causality", "pcr-mandated"
      ]
    },
    "primaryDataShare": { "type": "number", "minimum": 0, "maximum": 100 },
    "reportingPeriod": {
      "type": "object",
      "required": ["startDate", "endDate"],
      "properties": {
        "startDate": { "type": "string", "format": "date" },
        "endDate": { "type": "string", "format": "date" }
      }
    },
    "organization": {
      "type": "object",
      "required": ["orgName"],
      "properties": {
        "orgName": { "type": "string" },
        "orgId": { "type": "string" },
        "siteCountry": { "type": "string", "pattern": "^[A-Z]{2}$" }
      }
    },
    "dataQuality": {
      "type": "object",
      "properties": {
        "coveragePercent": { "type": "number", "minimum": 0, "maximum": 100 },
        "technologicalDQR": { "type": "number", "minimum": 1, "maximum": 3 },
        "temporalDQR": { "type": "number", "minimum": 1, "maximum": 3 },
        "geographicalDQR": { "type": "number", "minimum": 1, "maximum": 3 },
        "completenessDQR": { "type": "number", "minimum": 1, "maximum": 3 }
      }
    },
    "verification": {
      "type": "object",
      "properties": {
        "hasAssurance": { "type": "boolean" },
        "level": { "type": "string", "enum": ["limited", "reasonable"] },
        "verifierName": { "type": "string" },
        "standardRef": { "type": "string" }
      }
    }
  }
}

Section 7

OWL Turtle Formal Definition

The OWL Turtle representation provides the formal semantic grounding for COMET classes. OWL equivalence axioms link COMET terms to external ontologies (PACT, QUDT), enabling automated reasoning and cross-ontology alignment. SHACL shapes validate instance data against these class definitions at runtime.

OWL Turtle — COMET Class Definitions

@prefix comet-pcf: <https://comet.carbon/v1/pcf#> .
@prefix owl:       <http://www.w3.org/2002/07/owl#> .
@prefix rdfs:      <http://www.w3.org/2000/01/rdf-schema#> .
@prefix xsd:       <http://www.w3.org/2001/XMLSchema#> .
@prefix pact:      <https://wbcsd.github.io/pact/v3/ont#> .
@prefix qudt:      <http://qudt.org/schema/qudt/> .

comet-pcf:ProductCarbonFootprint a owl:Class ;
    rdfs:label "Product Carbon Footprint"@en ;
    rdfs:comment "ISO 14067 product-level carbon footprint result"@en ;
    owl:equivalentClass pact:CarbonFootprint ;
    rdfs:subClassOf [
        a owl:Restriction ;
        owl:onProperty comet-pcf:declaredUnit ;
        owl:cardinality 1
    ] .

comet-pcf:fossilGWP a owl:DatatypeProperty ;
    rdfs:label "Fossil GHG emissions"@en ;
    rdfs:domain comet-pcf:ProductCarbonFootprint ;
    rdfs:range xsd:decimal ;
    owl:equivalentProperty pact:pCfExcludingBiogenic ;
    qudt:unit qudt:KiloGM-CO2e .

comet-pcf:CBAMDeclaration a owl:Class ;
    rdfs:label "CBAM Declaration"@en ;
    rdfs:comment "EU CBAM embedded emissions declaration per Reg. 2023/956"@en ;
    rdfs:subClassOf comet-pcf:ProductCarbonFootprint .

comet-pcf:cnCode a owl:DatatypeProperty ;
    rdfs:label "Combined Nomenclature code"@en ;
    rdfs:domain comet-pcf:CBAMDeclaration ;
    rdfs:range xsd:string .

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