> ## Documentation Index > Fetch the complete documentation index at: https://docs.auth.energy/llms.txt > Use this file to discover all available pages before exploring further. # Retrieve individual CIM XML Difference Model file from a Development Project > Returns a single CIM XML Difference Model file (EQ, SC, or GL) from within a Development Project archive. Difference Models contain both forwardDifferences (additions) and reverseDifferences (deletions) against a base Full Model. ## OpenAPI ````yaml /neso-dsi/api/ltds_grid_modelling_openapi.yaml get /stage3/development-projects/{projectId}/{cimFile} openapi: 3.1.0 info: title: LTDS Grid Modelling Data Exchange API description: > API specification for the Long Term Development Statement (LTDS) Grid Modelling data exchange, as defined in LTDS Grid Modelling Annex 2 – Data Exchange Specifications Version 6 (published 22 February 2026). Data is exchanged as CIM XML (RDF/XML) files conforming to LTDS merged profiles derived from CGMES v3.0. Files are organised into .zip archives and published via a web page per licence area. This API covers: - Stage 2 publications (Fault Level, System Capacity existing & future year 1) - Stage 3 publications (NETS solved cases, Fault Level, System Capacity, Development Projects) Owned by Ofgem. Maintained by the GB CIM Advisory Group facilitated by BSI. version: 6.0.0 contact: name: GB CIM Advisory Group (facilitated by BSI) license: name: © Ofgem – All rights reserved servers: - url: https://ltds.{licenceArea}.example.com/grid-modelling description: > Per-licence-area LTDS publication endpoint. Replace {licenceArea} with the appropriate licence area code. variables: licenceArea: enum: - EPN - EMIDS - LPN - SPM - WMIDS - NPgN - SPENW - SHEPD - SPD - SPN - SEPD - SWALES - SWEST - NPgY default: EPN description: > Licence area code for the DNO: EPN=East England (UK Power Networks), EMIDS=East Midlands (National Grid Electricity Distribution), LPN=London (UK Power Networks), SPM=North Wales/Merseyside/Cheshire (SP Energy Networks), WMIDS=West Midlands (National Grid Electricity Distribution), NPgN=North East England (Northern Powergrid), SPENW=North West England (Electricity North West), SHEPD=North Scotland (Scottish and Southern Electricity Networks), SPD=South and Central Scotland (SP Energy Networks), SPN=South East England (UK Power Networks), SEPD=Southern England (Scottish and Southern Electricity Networks), SWALES=South Wales (National Grid Electricity Distribution), SWEST=South West England (National Grid Electricity Distribution), NPgY=Yorkshire (Northern Powergrid) security: [] tags: - name: Stage 2 Publications description: > LTDS Stage 2 publication endpoints. Covers Existing Fault Level, Existing System Capacity, and Future Year 1 System Capacity cases. - name: Stage 3 Publications description: > LTDS Stage 3 publication endpoints. Covers NETS Maximum/Minimum Demand solved cases, Fault Level, System Capacity (existing and 5 future years), and firm grid Development Projects. - name: CIM XML Files description: > Individual CIM XML file retrieval within a published .zip archive. Files conform to LTDS merged profiles serialised as RDF/XML. paths: /stage3/development-projects/{projectId}/{cimFile}: get: tags: - CIM XML Files summary: >- Retrieve individual CIM XML Difference Model file from a Development Project description: > Returns a single CIM XML Difference Model file (EQ, SC, or GL) from within a Development Project archive. Difference Models contain both forwardDifferences (additions) and reverseDifferences (deletions) against a base Full Model. operationId: getStage3DevelopmentProjectFile parameters: - name: projectId in: path required: true schema: type: string maxLength: 24 - $ref: '#/components/parameters/DevelopmentProjectFile' - $ref: '#/components/parameters/PublicationYear' - $ref: '#/components/parameters/Period' - $ref: '#/components/parameters/ZipVersion' responses: '200': description: CIM XML Difference Model file (RDF/XML) content: application/xml: schema: $ref: '#/components/schemas/CIMXMLDifferenceModel' '404': $ref: '#/components/responses/NotFound' components: parameters: DevelopmentProjectFile: name: cimFile in: path required: true description: CIM XML Difference Model file within a Development Project archive schema: type: string enum: - EQ.xml - SC.xml - GL.xml example: EQ.xml PublicationYear: name: publicationYear in: query required: true description: 4-digit calendar year of the LTDS publication schema: type: integer example: 2026 Period: name: period in: query required: true description: > 2-digit publication cycle number within the year. 01 = May publication cycle; 02 = November publication cycle. schema: type: string enum: - '01' - '02' example: '01' ZipVersion: name: version in: query required: false description: > Version number of the .zip file. Starts at 1 for the initial publication; incremented by 1 for each correction within the cycle. Independent of md:Model.version inside the CIM XML files. schema: type: integer minimum: 1 default: 1 example: 1 schemas: CIMXMLDifferenceModel: type: object description: > A CIM XML Difference Model file serialised as RDF/XML (IEC 61970-552). Describes grid changes as additions (forwardDifferences) and deletions (reverseDifferences) against a base Full Model. RDF namespaces used: - md: http://iec.ch/TC57/61970-552/ModelDescription/1# - dm: http://iec.ch/TC57/61970-552/DifferenceModel/1# - cim: http://iec.ch/TC57/CIM100# - eu: http://iec.ch/TC57/CIM100-European# - gb: http://ofgem.gov.uk/ns/CIM/LTDS/Extensions# - rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns# properties: header: $ref: '#/components/schemas/DifferenceModelHeader' forwardDifferences: type: array description: >- Grid objects/attributes/associations to be ADDED to the base Full Model items: $ref: '#/components/schemas/CIMObject' reverseDifferences: type: array description: >- Grid objects/attributes/associations to be DELETED from the base Full Model items: $ref: '#/components/schemas/CIMObject' required: - header DifferenceModelHeader: type: object description: > dm:DifferenceModel header as defined in IEC 61970-552 and the LTDS Header Profile. Appears at the beginning of every CIM XML Difference Model file. properties: mRID: type: string format: uuid description: Unique UUID identifier of this dm:DifferenceModel example: 39132026-9039-4a3f-9961-71F5529CEAA1 created: type: string format: date-time description: > Date/time the Difference Model was serialised (md:Model.created). Format: yyyy-mm-ddThh:mm:nn.nnnZ example: '2026-05-01T10:35:00.000Z' scenarioTime: type: string format: date-time description: > Anticipated in-service date/time of the development project (md:Model.scenarioTime). Format: yyyy-mm-ddThh:mm:00.000Z example: '2028-03-01T00:00:00.000Z' description: type: string description: Free-form description of the set of grid changes example: New 132kV substation and feeder additions – Project PROJ-NE-2026A modelingAuthoritySet: $ref: '#/components/schemas/LicenceAreaKind' version: type: string description: DNO-chosen version string, independent of .zip version number example: '1.0' profile: type: array description: Version IRI(s) of the LTDS merged profile(s) this file conforms to items: $ref: '#/components/schemas/ProfileVersionIRI' minItems: 1 dependentOn: type: array description: > UUIDs of other Difference Models on which this Difference Model depends. Zero to many entries. items: type: string format: uuid required: - mRID - created - scenarioTime - modelingAuthoritySet - profile CIMObject: type: object description: > A generic CIM grid instance object serialised in RDF/XML. All instances of classes inheriting from IdentifiedObject carry both an rdf:ID/rdf:about resource identifier AND an explicit cim:IdentifiedObject.mRID attribute. properties: mRID: type: string format: uuid description: > IdentifiedObject.mRID – present as both rdf:ID/rdf:about and as an explicit attribute value per IEC 61970-552. example: a1b2c3d4-e5f6-7890-abcd-ef1234567890 type: type: string description: > CIM class name (e.g. cim:ACLineSegment, cim:PowerTransformer, cim:EnergyConsumer, cim:GeneratingUnit, cim:Switch). example: cim:ACLineSegment name: type: string description: IdentifiedObject.name example: LINE-132-ALPHA-BETA description: type: string description: IdentifiedObject.description attributes: type: object description: > Profile-defined attributes for this CIM object, as key-value pairs where keys are fully-qualified CIM attribute names. additionalProperties: true example: cim:ACLineSegment.r: 0.1 cim:ACLineSegment.x: 0.4 cim:ACLineSegment.bch: 0 gb:ACLineSegment.ratedU: 132000 associations: type: object description: > Profile-defined associations as key-value pairs where values are rdf:resource references (UUIDs) to associated objects. additionalProperties: type: string format: uuid example: cim:ConductingEquipment.BaseVoltage: d9e8f7c6-b5a4-3210-fedc-ba9876543210 required: - mRID - type Error: type: object properties: code: type: integer example: 404 message: type: string example: >- Publication not found for the specified licence area, year and period. required: - code - message LicenceAreaKind: type: string description: DNO licence area code (gb:LicenceAreaKind) enum: - EPN - EMIDS - LPN - SPM - WMIDS - NPgN - SPENW - SHEPD - SPD - SPN - SEPD - SWALES - SWEST - NPgY example: EPN ProfileVersionIRI: type: string format: uri description: > Version IRI of an LTDS merged profile or CGMES v3.0 profile, as documented in the applicable .rdf file as owl:versionIRI. Available from the BSI GB CIM Engagement Hub. example: http://iec.ch/TC57/ns/CIM/CoreEquipment-EU/3.0 responses: NotFound: description: > The requested publication, archive or CIM XML file was not found. This may indicate the publication cycle has not yet been released, the parameters are incorrect, or no correction version exists. content: application/json: schema: $ref: '#/components/schemas/Error' ````