A data file contains actual data, or a view of the data. Records in data files are grouped into members. All the records in a file can be in one member or they can be grouped into different members. Most database commands and operations by default assume that database files which contain data have only one member. This means that when your program accesses database files containing data, you do not need to specify the member name for the file unless your file contains more than one member. If your file contains more than one member and a particular member is not specified, the first member is used.
Usually, database files that contain source programs are made up of more than one member. Organizing source programs into members within database files allows you to better manage your programs. The source member contains source statements that the system uses to create program objects.