Declare a column of data#

Decide whether a column of your data is a dimension, a relation or a parameter. What decides is what the math does with the column.

The column…	is declared as
is an axis: something is indexed by it, or an aggregation lands terms on it	a `dimension`
has one value per member of a dimension, or per tuple of several — a generator's bus, a line's two ends, a generator's zone by period	a `relation` with that `key`
relates members of two dimensions many-to-many, with nothing to weigh — which buses a generator may connect to	a bare `relation`, with no `values:`
relates members of two dimensions many-to-many, with a weight per pair — a link's efficiency to each bus, a cycle's lines	a `parameter` over both
is a label set the model only selects on or counts within — a period, a season, a zone	a `dimension`, and a `relation` onto it
scales terms — a coefficient, a bound, an offset	a `parameter` (`float` or `int`)
is a per-row attribute the math only selects on — a fuel, a constraint's sense	a `str` parameter
is a mask	a `bool` parameter

Two rules decide the cases the table does not list: