Path schema supports computed columns e.g

export schema '/clean/SalesOrders.ion' with
  schema Schemas.SalesOrders
  NetAmountEUR : number = forex(schema.NetAmount, schema.Currency,"EUR", schema.OrderDate)
  UnitPriceEUR : number = forex(schema.UnitPrice, schema.Currency,"EUR", schema.OrderDate)

This is a nice solution to save some file storage for redundant columns.