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Using System Fields on the User Interface
ABAP_BACKGROUND As system fields are defined using the syst structure in ABAP Dictionary, you can technically use them to define input fields in dynpros or in Web Dynpro.
ABAP_RULE Do not use system fields on the user interface Never use system field types to define input or output fields for dynpros or selection screens in application programs.
ABAP_DETAILS This rule is derived from the SoC rule and the use of data types rule. System fields are purely technical. Their semantic properties, are defined in ABAP Dictionary (documentation and other texts), do not allow meaningful use in the user dialogs of application programs.
Latest notes: Similarly, you can apply the rule only use semantically appropriate data types to the use of SYST structure components (for typing interface parameters of procedures). The semantic meaning of a system field (expressed in the short text) does not generally match the meaning of the parameter. ABAP_HINT_END
Example ABAP Coding
When the program PGL_SYSTEM_FIELD_ON_UI is executed, input fields for document output language are displayed on a classic dynpro. The first input field is declared with reference to data type syst-langu of system field sy-langu. The second input field is declared with reference to a semantically suitable ABAP Dictionary data type. The displayed F1 help clearly indicates that syst-langu is not suited for language fields in a user dialog. This is because the help only describes the behavior of the sy-langu field in a program. It does not describe the meaning of the language field in the relevant application. ABAP_EXAMPLE_END
