Oracle 11g database datafile addition to ASM without '+' sign

If you miss the '+' sign, there will be several scenarios:

1. db_create_file_dest is set and points to ASM (i.e: +DATA): The database will take 'DATA' as an alias and will create ASM file on the destination associated with the 'DATA' alias that will be located at the ASM +DATA root directory.
2. db_create_file_dest is set and points to filesystem: It should be quite obvious that you'll have a new 'DATA' file in the location pointed at the parameter.
3. db_create_file_dest is not set (worst scenario): The database will default to $ORACLE_HOME/dbs and create a datafile there with the name 'DATA'.

A final piece of advice: Set the db_create_file_dest to point to the ASM DATA disk group and remove the datafile name parameter from your command:

alter tablespace AKDATA add datafile size 100M AUTOEXTEND ON;

As you may know, even if you give a name to the datafile, when it's created on ASM, that name becomes an alias and the real filename is set by the ASM instance itself. 

Please comment if you have any other scenario and solution to offer.