You can use data description specifications (DDS)
to define physical and logical database files.
Defining a physical file using DDS
You use file-level, record-level, field-level, and
key-field-level entries to define a physical file with data description specifications
(DDS).
Defining a logical file using DDS
A logical file determines how data records are selected and defined
when read by an application program. A logical file can be a simple, multiple
format, or join logical file.