An element is also linked to the suppliers providing the service. For every element-supplier relation the user shall enter the rate and currency at which the service is charged, together with any of the following restrictions and validation:
- An expression through which the system will determine the quantity/frequency at which the cost is incurred. Expressions are mathematically valid formulas containing constants, operators, database functions and variables. Variables are user-definable tags that are substituted with numeric values by the system’s calculation module.
- Services might be provided either on arrival or departure at an airport, and so, for every rate, the user may specify whether the cost is incurred when landing or departing, or during both phases of a flight.
- The user may also specify a range of dates, time intervals, and days when the rate is applicable. Therefore, the airline can distinguish between peak and off-peak cost rates. For example, if the airline incurs a night landing surcharge at a particular airport within specific hours, this type of validity may be used to limit when the rate is applied.
- A cost element rate may also be linked to one or more of the following:
- Flight numbers
- Aircraft types
- Aircraft Tails