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.

Provenance

Several artefacts referenced here live on propdata.org.uk / trust.propdata.org.uk, a legacy developer site that carries OPDA copyright but was not authored or approved by OPDA (OPDA has no editing access). Its content is not necessarily wrong, but specific technical approaches it presents — notably Decentralised Identifiers (DIDs) and DIDComm — are not an OPDA / MHCLG / DPMSG-ratified approach. Such decisions still need to be explored, tested, and certified against the emerging Smart Data Guidebook and aligned to the DSIT Digital Verification Services standards before they can be treated as canonical.

The full stack

flowchart TB L1["`**Network** TCP/IP · IETF · HTTPS`"]:::external L2["`**Secure communication** HTTPS · DIDComm`"]:::external DID["`**W3C DID Core 1.0** identifier methods did:key · did:jwk · did:web`"]:::external DVSTF["`**DVSTF** UK Digital Verification Services Trust Framework`"]:::external VC["`**W3C VC Data Model** verifiable credentials 1.1 + 2.0`"]:::external PDTF_V2["`**SPDTF spec** VC-based property data`"]:::infra PDTF_API["`**PDTF OpenAPI** v1.1 / v1.2 / v1.3 / v2.0`"]:::infra SCHEMAS["`**PDTF JSON Schema** v3.6 (active) pdtf-transaction.json`"]:::infra OVERLAYS["`**Form overlays** BASPI v4 / v5 TA6 · TA7 · TA10 NTS · CON29R · PIQ RDS · LPE1 · OC1 · LLC1 · FME1`"]:::infra FORMS["`Underlying UK forms Law Society · BASPI · NTS · HMLR · CON`"]:::data L1 --> L2 L2 --> DID L2 --> DVSTF DID --> VC DVSTF --> VC VC --> PDTF_V2 PDTF_V2 --> PDTF_API PDTF_V2 --> SCHEMAS SCHEMAS --> OVERLAYS FORMS -.shape.-> OVERLAYS

The PDTF schema and semantic-evidence 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 (2025). Frontend + Firebase backend. Moverly is since a former member.	—

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 and methodology references

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

DVSTF

Digital Verification Services Trust Framework (the rename of the former DIATF). Strategic alignment partner.

Linux Foundation

Trust Over IP (ToIP)

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

ISO · candidate method

ISO 23386:2020

A methodology for governing construction data attributes and characteristics in interconnected data dictionaries. It is relevant to OPDA's glossary, dictionary, vocabulary and mapping process, but is not yet an adopted conformance requirement.

Method, not model content

ISO 23386 uses property for a data attribute or characteristic, not for a real-estate asset. It defines how those properties and groups should be described and maintained; it does not supply their domain definitions or a construction ontology. OPDA can therefore use it as process evidence while the working groups remain responsible for agreeing the meanings needed by each bounded context. See the annotated entry in External references.

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.