ORA-39170: Schema expression 'PUBLIC' does not correspond to any schemas.Well, isn't the error clear enough ?
the command I used :
C:\Documents and Settings>expdp directory=export_dump_dir dumpfile=public.dmp logfile=public_exp.log schemas=PUBLIC parallel=2
PUBLIC is a role.
$ oerr ora 39170 39170, 00000, "Schema expression %s does not correspond to any schemas." // *Cause: A schema expression or schema list was supplied for a Data Pump // job that did not identify any schemas in the source database. // *Action: Correct the schema specifications and retry the job. $