User-defined data types can be stored for all programs in the ABAP Dictionary. These user-defined types provide the same functionality as the local types that can be defined in ABAP programs with TYPES (see Data Types and Data Objects).

The types defined globally in the ABAP Dictionary can be accessed in ABAP programs with TYPE. You can also refer to the types defined in the ABAP Dictionary when defining the type of a function module interface.

The central definition of types that are used more than once in the ABAP Dictionary permits them to be changed centrally. The active ABAP Dictionary ensures that such changes are made at all the relevant locations. ABAP programs, for example, are adjusted to the modified type definitions when they are recreated. If a type is changed, all the objects (e.g. types or tables) that use this type are determined at activation. The objects that are found are automatically adjusted to the change.

All types have a runtime object. This runtime object is generated the first time the type is activated and is adjusted to the current type definition at each further activation.

You can enter semantic information for a type in the type definition in the ABAP Dictionary. This includes for example text that is displayed for the F1 help, text for use in screens, search helps, and technical documentation.

There are three different type categories:

• Data elements (elementary types and reference types).
• Structures (structured types): A structure consists of components that also have a type, that is they refer to a type.
• Table types: A table type describes the structure and functional attributes of an internal table. A special case is the ranges table types.