Abstract: A user friendly interface system enables a user to incorporate, in an executable application, custom decision logic in the form of an expression involving a high-level script language. A system for providing a user interface display image supporting user entry of an expression involves a user interface menu generator for providing a displayable image. The displayable image includes a first image window listing a plurality of selectable data items available for incorporation in an expression as well as an image prompt element. The image prompt element permits user entry of the expression and incorporation of a data item in an entered expression from the listed data items to provide a resultant expression in response to user selection of the data item in the first image window. The displayable image also includes an icon for initiating storing of the resultant expression.