Since the database consists of single files with names corresponding to time down to the second as well as the event type (L, R or D) it will sometimes happen that two events will get the same name. Thus copying in a new event with the same name could overwrite the existing event, and the user would never know. In SEISAN, from version 5.0, some security has been put in. New data can enter the database with 4 programs: SPLIT, EEV, MULPLT and AUTOREG. With all programs, the user will be prompted if a new event is about to overwrite an existing event. Both SPLIT and EEV have the possibility to create alternative ID's if the user wants both the new and old event, while MULPLT and AUTOREG just offers the possibility to skip a double event. If a new ID is created, an attempt will be made to use a time one second later. If that also corresponds to an existing event, the next second is attempted etc. This allows for 60 events to be registered in the database with the same minute and event type. If an event has got the ID changed, the header line in the file is NOT changed, however the ID line is of course changed. This will be indicated on the ID line with a `d' at the end of the ID number.
Event here means S-file in the database. Events are only deleted when using EEV, either with the EEV delete command D or the EEV append command A. In both cases, the deleted event is stored in the DELET database before being deleted from whatever database. Even if the system contains many databases, there is only one DELET database. This means that deleted events from different databases are mixed in DELET. In order to restore an event, enter DELET database with EEV and copy the deleted event back with the C command. It is up to the user to manually clean up the DELET database.
There is one more final security. If an event has been deleted from a database, but an UPDATE has not yet been made, the event might be in the CAT part of the database and can be extracted by SELECT or the editor.