A data dictionary is a document that specifies, for every field and metric, exactly what it means, how it is calculated, where it comes from, and who is responsible for it. It solves a problem that looks technical on the surface but is actually organisational: sales, marketing and finance use the same words for different things, so they cannot agree on figures in meetings. An example is active customer, by which some mean someone who has purchased within the last year, and others someone who has a valid contract. The dictionary therefore contains the name, a verbal definition, the exact calculation including what is not counted in it, the data source, the update frequency, and the owner. Keep it in one place, accessible to everyone, and date every change to a definition so that figures remain comparable over time.
See also: Master data management, Data quality in analytics, KPIs for a marketer.
