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APPSI glossary of Open Data and PSI terminology


APPSI is the Advisory Panel on Public Sector Information (PSI), a non-departmental public body of the Ministry of Justice. Its role is to provide advice to Ministers, the Director of OPSI and Controller of HMSO. It responds to relevant events and government consultations and comments on draft government papers and legislation.   In this work it became apparent to APPSI that there was no consistent vocabulary for dealing with PSI or Open Data and this has sometimes caused confusion and misplaced emphasis.

The National Archives has produced a comprehensive glossary to inform the UK Government Licensing Framework for PSI. Certain terms have a specific meaning, defined in legislation and some are words that are well defined in dictionaries. However, rather than re-using stable definitions, it is observed that terms are often re-defined for documents produced by other organisations. In order to ensure consistency of definitions in its own deliberations, and encourage consistency across government, APPSI, in cooperation with the Cabinet Office, initiated an exercise to aggregate and rationalise glossaries into a single preferred set of definitions.

Rather than decide on the most appropriate definitions internally, it was felt that the proposed definitions themselves should be offered to the wider PSI and Open Data communities for comment using a 'wiki' style mechanism - a site that allows multiple contributions to be combined to arrive at a consensus view of what is the most appropriate definition. Following a recommendation in the Open Data White Paper 2012 (Cm 8353), the Cabinet Office has been working with APPSI to make a 'wiki' style site available to consult on the definitions proposed. This is now available at


The initial glossary has been compiled from six glossaries from government documents and open data organisations. In addition APPSI and the Cabinet Office have added some definitions from other official sources and from our own deliberations. A cumulative list of preferred terms from all the sources has been assembled.

Definitions have been graded by members of the team as follows:

***** Widely agreed definition or enshrined in legislation
**** A sound definition; fit for purpose
*** A working definition capable of improvement
** Usable but potentially confusing or ambiguous
* A loose or contentious definition; not adequate

The glossary at will be lightly moderated by members of APPSI and managed by the Cabinet Office. Terms already defined in legislation or regulations will be identified specifically and these official definitions will not normally be changed. Where appropriate, a more colloquial definition of a legal term may be included in the main glossary, but such definitions will be annotated to point to the formal legal definition.  

APPSI will also consider and incorporate, where appropriate, suggestions in its own cumulative glossary. The APPSI glossary will be revised from time to time and version numbered.   Users are welcome to make any comments on the list by email to


The status of the glossary is advisory. However it should become normal good practice not to use defined terms loosely or to publish other PSI or Open Data glossaries without first referring to the glossary. Terms should not be re-defined without good reason, and where terms are, or need to be, re-defined, the reasons should be placed on the Cabinet Office wiki site or sent to APPSI.

It is hoped that the glossary will bring a much-needed degree of clarity to discussions and publications relating to the handling of PSI and Open Data.