What is the Taxonomy Best Practice Framework?

The Taxonomy Best Practice Framework provides principles against which taxonomies suitable for use across government can be evaluated.

The framework aligns to the Code of Practice for Statistics, which is based on three pillars: trustworthiness, quality and value.

The Taxonomy Best Practice Framework is a product of the Taxonomy Oversight Group (TOG).

TOG was established as part of a joint project between the Office for National Statistics (ONS) and the Central Digital and Data Office (CDDO) within the Cabinet Office. 

The group brings together taxonomists and data management experts from across government. 

TOG provides expert knowledge to discuss, review, assess and make recommendations on taxonomies that are suitable for use across government.

You can download a copy of the Taxonomy Best Practice Evaluation Framework (PDF, 599.1KB).

If you would like more information on TOG please contact the Taxonomy team on TOG@ons.gov.uk.

Principles of a good taxonomy


A taxonomy is the result of naming and classifying items into groups within a larger system according to their similarities and differences. The resulting terms structure, which can be either flat or hierarchical in nature, is used to provide a conceptual framework for discussion, analysis or information retrieval.


There must be clarity about the role of the taxonomy in a specific circumstance. What is the problem that the taxonomy is trying to resolve? A good taxonomy should be built with the end user in mind. It must be regularly updated, relevant and sufficiently detailed to be fit for purpose. If end users find that the taxonomy fails to meet their requirements, they may amend or substitute categories for their own purposes, thereby reducing the overall comparability and relevance of the taxonomy.


The level of complexity must adequately reflect end user requirements, with challenge given to any additional level of detail within the taxonomy that does not have a compelling purpose. An unnecessarily complex taxonomy has the potential to negatively impact adoption.

Everything should be made as simple as possible, but no simpler.

Albert Einstein


Does the taxonomy have a sense of balance? If some high-level groupings have just two or three sub-categories while others have considerably more, this could reflect user need or may be a sign that the balance of the taxonomy requires further consideration.

Exceptions to this may include "Country", and other unambiguous long lists, which can be presented alphabetically. Care must also be taken to ensure that there are no "empty" categories within the taxonomy.

Ownership and governance

There must be a clear owner of the taxonomy and governance policies in place for maintaining and updating the structure. It is the responsibility of the owner or custodian to maintain the classification in line with any agreed national or international process for revision, update and amendment. This responsibility includes maintaining any supporting materials associated with the taxonomy. Governance policies should define who does which tasks, procedures for performing tasks, and feedback mechanisms for suggesting changes and improvements.  


The taxonomy and supporting materials must be hosted in an appropriate location with clear signposting to direct users to its location. It should be available in accessible downloadable formats that are suitable for user needs. Materials should be provided in plain English and use language appropriate to user needs.


The taxonomy must, where possible, adopt and align to existing national and international standards including those of devolved administrations. A new taxonomy should have the ability to map to existing sources enabling the accurate, effective and consistent exchange of data between sources. Detail should also be provided where any instances of overlap with alternative taxonomies occur.  


The taxonomy should be supported by additional materials such as detailed scope notes. This will ensure that new terms that are synonyms for existing categories are correctly recorded and not otherwise added as new categories.

A single term with a definition overlapping that of another term, or a misplaced hierarchy, can disrupt the whole taxonomy. Therefore, no new term should be added to a taxonomy without a formal approval or review process.

Well-defined terms

The terms within the taxonomy should strive to be unambiguous and mutually exclusive. The taxonomy must also provide a structured way of handling terms that do not fit into a prescribed category. This includes the provision of adequate space in which to attribute those entries classified as n.e.c. (not elsewhere classified) or n.o.s. (not otherwise specified). Failure to do so may result in an inability to assign data or an unmanageable "miscellaneous" category containing dissimilar entries.

Revision and maintenance

A successful taxonomy must have a regular revision and maintenance process in place. This must be undertaken in a timely manner to account for change. An ongoing commitment of resources will be required to ensure that it remains relevant and fit for purpose.

All changes should go through a defined review process. There should be no ad-hoc or knee-jerk reactions to user requests for changes to the taxonomy. Any and all changes must be clearly labelled and communicated to enable accurate cross-reference.


Metadata are a set of data that describe and give information about other data. It is crucial that appropriate metadata are recorded about the taxonomy. Metadata provide a structured reference and can cover a wide range of topics.

Typical examples would be: Title, Subject, Description, Coverage, Date, Creator, Format, and so on.


The method by which a taxonomy was derived must be freely available to users. Open code used to inform the taxonomy should be made available where possible as should details of individuals that contributed via committee to the taxonomy development.

Engagement strategy

There must be a clear strategy in place to provide users with adequate opportunity to contribute to the revision cycle and communicate any changes in the taxonomy. All users should be made aware of the review or revision process and encouraged to participate in any stakeholder engagement. Updates must be provided regularly and should include details of any "New Terms", "Deleted Terms", "Merged Terms" and "Split Terms". Any changes to the structure, content or methodology of the taxonomy should be communicated as early as possible to allow users sufficient time to prepare for implementation.


Over time new content will appear, which will need to be assimilated into the taxonomy. A successful taxonomy must have the scope to incorporate new or emerging elements. Without sufficient forward planning in place the original, well-structured taxonomy may quickly become outdated. Careful consideration of each of the principles outlined, alongside expert, topic-specific knowledge, will help to ensure the long-term effectiveness of the taxonomy.

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