The use of IDEA is incomplete without Field Manipulation.
One of the utilities of Field Manipulation is to allow the user to append/add fields to the active database. This is required to create a new field with recalculated values, derived values, conditional values and more like arriving at the delay in days for levy of penal interest as an example.
Here it is vital to understand the difference between native fields and virtual fields.
Native fields are fields which are part of the source data duly imported to IDEA. These are static values and form part of the active database. These are fields which are used to recalculate or recompute or recondition derived values.
So this brings us to virtual fields. Virtual fields are derived fields and dynamic in nature. They derive their value through a condition/equation/parameter/criteria applied on native fields.
So as an example if I import a source file containing 'Instalment Due Date' and 'Instalment Overdue Paid Date' into IDEA. These fields are the native fields forming part of the original source data.
Using these fields when I create a field titled 'Penal Interest' with the criteria 'Instalment Amount * @age(Instalment Overdue Paid Date, Instalment Due Date) * penal interest/36500' the field 'Penal Interest' represents the virtual field or derived field.
Users can always revisit a virtual field and go through the equation applied during the life cycle of the database. The equation gets stored in the file and is visible in Field Manipulation plus History.
Virtual fields appear with a different font colour in the active database for a visual segregation between the native and virtual fields.