  Spreadsheets often have variables and formulas that are similar, differing
only by the fact that they refer to different instances of an entity. For
example, the calculation of the sales revenues of the South and East regions
are Revenues South = Price * Quantity Sold South and Revenues East = Price *
Quantity Sold East. In this paper, we present a conceptual modelling approach
that takes advantage of these similarities and leads the spreadsheet developer
to the formula Revenues = Price * Quantity. We then present simple but strict
rules to implement the spreadsheet.
