Which predefined ABAP type is considered incomplete?

The predefined ABAP type that is considered incomplete is the type P. This type is known as 'packed number' and is defined in ABAP as a fixed-length decimal number that can store up to 31 significant digits and has an implied decimal point. The incomplete nature of the type P arises from its lack of a fixed-length definition, meaning that the total number of digits it can hold can vary depending on the application context and how it is utilized.

Packed numbers can be defined with different lengths, but without specifying the exact character length, it is not a complete type specification like others, which have a well-defined set length (e.g., STRING or XSTRING). As a result, packed numbers require clear specifications when used in declarations, placing them in the category of incomplete types.

On the other hand, STRING and XSTRING are complete types used for variable-length character and binary strings, respectively, while F refers to floating-point numbers, which also have a defined structure and behavior in ABAP. Therefore, P distinguishes itself as an incomplete type due to its variable nature and need for explicit length detail when utilized in coding.