The Transformation Library and Formula Builder 
The Transformation Library and Formula Builder
Use
A transformation library is available in the maintenance for transfer rules for an InfoSource, and in the update rules for a data target. You can use this in connection with the formula builder.
Do not use formulas for RemoteCubes, because inversion is not allowed for them. Use routines in this case.
Functions
The transformation library, in collaboration with the formula builder, enables you to easily create formulas, without using ABAP coding.
The transformation library has over 70 pre-defined functions, in the following categories:
In the dialog box to select an update method, you can use the information pushbutton 
to get a list of the available functions with a description of their syntax.
You also have the option to implement self-defined functions in the transformation library of the formula builder. You can integrate existing function modules in these self-defined functions. In doing so, you can also make available special functions to be used frequently that are not contained in the transformation library. Refer to
BAdI: Customer-Defined Functions in the Formula Builder.The formula builder has two modes: Standard and expert mode. In the standard mode, you can only enter the formulas using the pushbuttons and by double clicking on functions and fields. In the expert mode, however, you can enter formulas directly. You can also toggle between the tow modes when entering a formula.
You can find more detailed operating instructions for the formula builder by means of the information button .
You can find a step-by-step guide using an example under
Example for Using the Formula Editor.