You use the hierarchy of a form class to display and model the data of an application or process. All of the form levels together, that is, all nodes of the hierarchy, reflect the maximum quantity of data that an application supports for use in forms as standard.
You transfer the hierarchy of a form class to the application forms. There you can configure the form as required. Using defined data areas, you can transfer the data declared in the form class to a form.
The hierarchy consists of two node elements: The form levels and the 1:1 levels. Each form level and 1:1 level represent a data structure that is dependent on data that is higher in the hierarchy in accordance with its hierarchical position. The individual fields of a form level or 1:1 level are defined by an assigned DDIC structure. For each level there are subroutines (ABAP form routines) in the form class library that carry out encapsulated data selections in the relevant tables of the database.
The following figure shows the hierarchy of a form class using the standard example delivered, PWB_FLIGHT_NOTIFICATION.
The hierarchy is a major component of a form class. The fixed assignment of the form class in an application form means that the hierarchy defined in the form class is always the template for the hierarchy in the application form and is always compared to it.