Modelling Updated 2026-05-14

Standards stack

What OPDA actually publishes — the technical artefacts that implement the wider UK initiative's intent. Five layers from identity primitives up through UK-form-specific schema overlays.

The full stack

flowchart TB classDef opda fill:#1a4d80,color:#fff,stroke:#0b2545,stroke-width:3px; classDef ext fill:#eef4f8,stroke:#1a4d80,color:#0b2545; classDef form fill:#fef3c7,stroke:#b45309,color:#7c2d12; L1["Network
TCP/IP · IETF · HTTPS"]:::ext L2["Secure communication
HTTPS · DIDComm"]:::ext DID["W3C DID Core 1.0
identifier methods
did:key · did:jwk · did:web"]:::ext DIATF["DIATF
UK Digital Identity &
Attributes Trust Framework"]:::ext VC["W3C VC Data Model
verifiable credentials 1.1 + 2.0"]:::ext PDTF_V2["PDTF v2.0 spec
VC-based property data"]:::opda PDTF_API["PDTF OpenAPI
v1.1 / v1.2 / v1.3 / v2.0"]:::opda SCHEMAS["PDTF JSON Schema
v3.6 (active)
pdtf-transaction.json"]:::opda OVERLAYS["Form overlays
BASPI v4 / v5
TA6 · TA7 · TA10
NTS · CON29R · PIQ
RDS · LPE1 · OC1 · LLC1 · FME1"]:::opda FORMS[Underlying UK forms
Law Society · BASPI · NTS · HMLR · CON]:::form L1 --> L2 L2 --> DID L2 --> DIATF DID --> VC DIATF --> VC VC --> PDTF_V2 PDTF_V2 --> PDTF_API PDTF_V2 --> SCHEMAS SCHEMAS --> OVERLAYS FORMS -.shape.-> OVERLAYS

The PDTF standards stack. Blue boxes = OPDA-owned; light boxes = external standards; amber = UK industry forms.

The five GitHub repositories

Repo	Default branch	What it contains	Live deployment
`schemas`	`master`	PDTF JSON Schema v3.6 (current) + overlays. Published as `@pdtf/schemas` on npm.	trust.propdata.org.uk (GH Pages)
`api`	`main`	OpenAPI specs (v1.1 JSON, v1.2 YAML; v1.3 + v2.0 in `web/public/api/`)	—
`trust-framework`	`main`	Spec docs (Property Data Trust Framework 2 Specification, DID Auth OAuth 2 Spec), governance docs, examples	Mintlify docs (referenced from web)
`web`	`main`	Astro + Starlight site source. Bundles schemas + API specs as static assets.	propdata.org.uk (GH Pages)
`smart-data-challenge-2025`	`main`	Moverly + OPDA SDC entry. Frontend + Firebase backend.	—

All five cloned at source/03-standards/ and source/06-research/smart-data-challenge/code/ and source/07-website/source/.

Schema version state

Version	Status	Notes
v1	Legacy	Property-grouped schemas (legal-information.json, title-deed.json etc.)
v2	Stable	Single `pdtf-transaction.json` + overlays
v3 (current 3.4 stable)	Stable	Modular overlay system; supports BASPI overlay composition
v3.6	Active development	Per propdata.org.uk about page

Schema overlays (form coverage)

The overlay system is the cleverest part of PDTF — a single base pdtf-transaction.json schema, plus stackable overlays for each UK industry form. Overlays merge into the base via custom deep-merge logic.

Overlay	What form / source	Status
`baspi.json` / `baspi5.json`	HBSG Buyer and Seller Property Information (v4 / v5)	Active — both supported
`ta6.json`	Law Society TA6 Property Information Form (6th ed, 2025)	Active
`ta7.json`	Law Society TA7 Leasehold Information Form (5th ed, 2025)	Active
`ta10.json`	Law Society TA10 Fittings and Contents Form	Active
`nts.json`	NTS Material Information rules (Sales / Lettings v1.0)	Underlying rules withdrawn — awaits MHCLG replacement
`con29R.json`	CON29R Residential search form	Active
`con29DW.json`	CON29 Drainage and Water	Active
`piq.json`	Property Information Questionnaire	Active
`rds.json`	Residential Data Schema	Active
`lpe1.json`	LPE1 Leasehold Property Enquiry	Active
`oc1.json`	OC1 Office Copy entries (HMLR title)	Active
`llc1.json`	LLC1 Local Land Charges search	Active
`fme1.json`	FME1 Form for Mortgage Enquiries	Active

All overlay files at source/03-standards/schemas/src/schemas/v3/overlays/ (current) and v2/overlays/ (previous version).

API specifications

Version	Format	Status	Location
v1.1.0	JSON	Released	`api/pdtf-api-1.1.0.json`
v1.2.0	YAML	Released	`api/pdtf-api-1.2.0.yaml`
v1.3.0	YAML	Active — bundled with web redesign	`api/pdtf-api-1.3.0.yaml`
v2.0.0	YAML	Active — VC-based	`api/pdtf-api-2.0.0.yaml`

Identity / participants

Participants in the PDTF ecosystem use W3C DIDs:

did:key:... — used for examples in the trust-framework repo
did:jwk:... — JSON Web Key DID method
did:web:... — domain-anchored DIDs (likely for OPDA-accredited members)

Example participants in the public test infrastructure are at source/07-website/source/public/trustframework/api/members/did:*.

External standards alignment

W3C

Verifiable Credentials Data Model 1.1 + 2.0

The provenance/verification foundation. Locally archived for offline reference.

W3C

Decentralized Identifiers 1.0

How participants are identified. Archived as did-core.html.

UK Gov

DIATF

Digital Identity and Attributes Trust Framework. Strategic alignment partner.

Linux Foundation

Trust Over IP (ToIP)

The 4-layer governance model PDTF follows. See ToIP governance.

Where to start (for the linked-data project)

For the semantic modelling work, three artefacts are essential reading first:

source/03-standards/schemas/CLAUDE.md — how the overlay system works, merge semantics, validator patterns.
source/03-standards/trust-framework/CLAUDE.md — the Trust Framework spec, governance, examples, Mintlify docs.
source/03-standards/trust-framework/docs/Draft_ Property Data Trust Framework 2 Specification.md — the formal spec being prepared for v2.0.