Every ABAP developer will write an application log some day. SAP system provides wide range of logging and monitoring capabilities from simple tools to sophisticated ones. SAP is restructuring the different applications and functions encapsulated in packages to specific layers and and application components from time to time. Audit Information System ( AIS ) is part of the SAP basis, so this component is available in every ABAP System (at least from 7.0 EhP2). This contains class
cl_s_aut_bal_log what you can use to create Application Logs and save (or display).
DATA(lo_applog) = cl_s_aut_bal_log=>create( im_object = 'Some_Object' im_subobject = 'Some_subobject' ).
Lack in this that this does not provide the external ID as parameter, but this not necessery in all cases.
You can read more about Application Logging - Auditing and Logging in SAP Library.