You can use the wildcard character (*) to reference tables using an alias.
s.* aliases the staging table
I.* aliases a temporary table and provides ROWID_OBJECT, PKEY_SRC_OBJECT, and ROWID_SYSTEM information for the records being updated. The i alias can only be used for ROWID_OBJECT, PKEY_SRC_OBJECT, and ROWID_SYSTEM columns in a validation rule.