The following schema names are reserved:
In addition, it is strongly recommended that schema names never begin with the SYS prefix, as SYS is by convention used to indicate an area reserved by the system.
No user-defined functions, user-defined types, triggers, or aliases can be placed into a schema whose name starts with SYS (SQLSTATE 42939).
It is also recommended not to use SESSION as a schema name. Declared temporary tables must be qualified by SESSION, so it is possible to have an application declare a temporary table with a name identical to that of a persistent table, complicating the application logic. To avoid this possibility, avoid using the schema SESSION except when dealing with declared temporary tables.