Complete Oracle System (Instance & Database) Design: Steps of Implementation - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 129

Figure 6-3: Planning database files location and naming. OFA defines
standard directory architecture whereas OMF defines standard file
naming convention. Oracle Flexible Architecture (OFA) defines the
standard directory architecture for Oracle physical files. Oracle
Managed Files defines the naming conventions for Oracle physical
files. If use DBCA to create the Oracle database then you don't have to
worry about OFA and OMF. DBCA follows OFA and OMF
automatically.