The Vision of Britain system holds a large library of historical statistics. We store all the data values in one big list, and for each value we record:

• WHERE the data value is for, by links to our administrative gazetteer
• WHEN the value is for, by a year or period
• The SOURCE, linking to our listings of Census Reports

We record WHAT each number measures via our implementation of the Aggregate/Tabular Data Extension developed by the Data Documentation Initiative. This places each data value within an nCube whose dimensions are defined by variables (sometimes organised into variable groups), like occupation and gender and age, each of which is a set of categories, such as "Males" and "Females":

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The implementation is structured as an ontology containing 6,152 entities of the following types, linked by 19,427 relationships:

Entity type	Entities in system
Databases	1
Themes	10
Rates	63
nCube Groups	12
nCubes	184
Variable Groups	16
Variables	169
Categories	5,623
Measurement Units	14
Universes	60