The representations available for each category are defined by the Global Schema. Every category has at least one representation, and many have more than one.
At its simplest, a representation is a standardised way of formatting values. For example, two datasets might use different date formats in their original data, but the standardised representation of a date will be the same for both of them.
But some representations do more than that - reflecting interpretation or analysis of an item of data. For example, the category called
Occupation has representations called
Seniority. In this way, the complex and multi-faceted information contained in a job description is broken down into specific details, which can then be accessed in queries and reports.