as4/dbmon/classic is a SAP Parameter attribute which is used to control switch between classic DB monitor and plan cache dump information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
If this profile parameter is set to 0 the plan cache dunmp will be
used for collecting information about database performance. If the
parameter is set to 1 the classical DB monitor will be used.
See SAP Note 1083218 for details.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.