(last updated Oct 2022)
There have been several attempts to use technology to improve the poor consumer experience of buying and selling residential property in the UK. The reasons these have not been successful are varied, but commonly they have sought to create a new single, proprietary digital platform on which all transactions must be conducted. Due to the highly fragmented nature of the industry, it has not yet been possible to secure sufficient adoption for market dynamics to encourage all stakeholders to participate.
In setting out the Property Data Trust Framework (PDTF), we seek to propose a set of data, interface and governance principles that put the consumer (buyer and seller) at the heart of the process and allow participants to share data and coordinate transactions in a platform- and technology-agnostic manner. We believe this openness and transparency will provide the right conditions for broad industry adoption.
This document is designed to outline the framework and how it will evolve, to identify the roles and responsibilities of the various participants and to outline the technical principles that framework implementations should follow.
The Property Data Trust Framework will enable people and organisations to use and reuse information relating to a property. It will give them a way to access and share verified property information or “property attributes” with other people and organisations more easily.
The trust framework is a set of data standards, technical standards, and process rules that different organisations agree to follow to deliver one or more of their services. This includes legislation, standards, guidance, and the rules.
By adopting these standards, all services and organisations using the trust framework can describe property information they’ve created in a consistent way. This will make it easier for organisations and users to complete property transactions or share information with other trust framework participants.
The aim is to create a framework that is:
The implementation of the PDTF development process is split into two parts:
This document relates only to the first of these parts.
The initial use case of the framework is to provide interoperability around the Home Buying and Selling Group’s ‘Property Pack’ concept, which incorporates the existing Buyers and Sellers Property Information (BASPI) dataset as well as Title Deed, Energy Performance Certificate and Property Searches data.
It is the intention of the framework that residential property transactions across the UK should be supported. However in this early phase the schemas are limited to the data requirements of transactions in England and Wales.
It is recognised that framework governance will play an important role as the ecosystem of participants grows. At this early stage, we identify that concerted effort will need to be made to develop governance principles around:
The framework aims to support all the various stakeholders in the process, the roles in the process can be defined at a high level in four key categories (shown above):
Data providers are expected to:
The Framework combines:
In accordance with our goal of making implementation of the Framework as straightforward as possible, the following Open Standards are employed:
A key principle of the framework is that both the history and the provenance of the data is represented. To achieve this, it is necessary to prevent direct changes to the data itself, but instead store the changes as a series of ‘claims’, with associated provenance data.
To generate the current state of the data, it is necessary to successively apply the changes made in each claim to an initial blank data object. In this way a claim made against a particular part of the data structure can be replaced by later data, but the history and the provenance of each claim can always be available.
The Framework uses a number of interdependent JSON Schemas to represent the full range of property data. A root schema represents the overall Property Pack, with subschemas for individual pack elements being referenced from there.
This decomposition also allows for independent modelling of data which persists across property transactions (the Energy Performance Certificate, for example) as well as the more transient aspects of the sale itself.
A publicly-accessible Git repository for these schemas is at https://github.com/Property-Data-Trust-Framework/schemas.
Well-managed versioning of framework schemas is very important, both in the early stages of framework development when there are likely to be many changes, but also when it has been more widely adopted, at which point there will be numerous software and services providers relying on consistent behaviour.
Framework schemas are labelled using Semantic Versioning as Major.Minor.Patch (e.g. “1.3.5”) where it is clear whether changes are backwards-compatible bug fixes (Patch increment), backwards-compatible but with new functionality (Minor increment), or a non backwards-compatible, breaking change (Major increment).
With care, it should be possible to significantly evolve the capabilities of the framework while still maintaining backward compatibility with earlier schema versions. In particular, it should rarely be necessary to add in additional ‘required’ properties to top-level elements which might invalidate existing data.
Data provided using older schemas will still be valid against newer ones (from the same Major version) and older software can silently ignore the new data until they’re ready to make use of it.
One of the key elements of the Framework is the requirement to attach provenance information to each element of property data.
The OpenID Connect ‘verified claims’ model is used, which not only provides a standards-based way to represent the accompanying evidence, but also provides a way of representing elements like verified identities in a way which is already supported by identity service providers and recognised by relying parties.
The Framework extends the ‘claims’ object of the verified claims model with a PDTF Claims Schema, allowing for the representation of important schema version, data path information (where in the model does the supplied data belong) and attribution/licensing information. Within the verified claims model, the following are additional requirements for PDTF claims:
The ‘evidence’ element of the verified claims schema supports the representation of varying levels of provenance evidence:
Any valid evidence element is permitted, and it is up to the business logic of the participants to determine whether the evidence is sufficiently strong to meet users’ requirements. For example, it may be acceptable that the property seller vouches for the state of the solar panels on their roof, but that the Title Deeds must come in electronic form directly from HM Land Registry.
The API is specified using the OpenAPI Standard and in accordance with REST-ful principles. Mutability of the property data, or of historical claims, is not permitted; claims can only be added and the resulting property data state queried.
OpenID Connect is primarily intended for claims about identity. As such, the data model within the claims object itself does not support the metadata necessary to identify the schema, path and attribution aspect of exchanging property data.
A PTDF-claim JSON Schema is supplied, against which claims embedded in the OpenID Connect verified claims object should be valid.
For the vast majority of use cases it is sufficient to reference a property using its Unique Property Reference Number (UPRN), a unique identifier for every addressable location in Great Britain. The current schemas and API specification use UPRN as a natural primary key to identify both the property and the residential transaction.
However it is also possible that what a user considers to be a ‘property’ may comprise more than one UPRN, and that a residential sale may comprise the transfer of one or more Title Deeds that don’t directly correspond to a single UPRN.
It is envisaged that support for composite primary keys of UPRNs and Title Numbers will be added in the near future.
In accordance with the restrictions on mutability of claims, the following endpoints are represented in the API Specification:
It should be possible to recreate both the current state and the provenance map given just the set of claims, but these endpoints are supported for convenience anyway. Security
The PDTF Open API specification does not currently mandate security methods. However it is likely that the specification, or the framework governance model, may require:
The PDTF API is also versioned using Semantic Versioning. It is intended that future changes be made through extension of the existing specification, to retain backward compatibility with earlier versions. Over time, legacy versions may become deprecated but capabilities will only be removed when participants have had plenty of time to migrate their implementations.
A publicly-accessible Git repository for the API Specifications is at https://github.com/Property-Data-Trust-Framework/api.