The file must include a header row, and the header must include a column named “time” followed by the variable names. Everything to the left of time is a subscript dimension, and everything to the right is a variable.
Normally, subscripts will be in the leftmost columns, so the variable headers will be unsubscripted variable names. However, you can subscript the variables instead, in which case Time will be the first column. So, either:
<city><Time><price of cheese><tax rate>
<Time><price of cheese[boston]><price of cheese[Detroit]><tax rate[boston]><tax rate[Detroit]>
<3><5>< ><.2>< >
<4>< ><4>< ><.2>
The first option is typically preferred for clarity and space efficiency.