Concatenation can be thought of as processing a sequence of like or unlike data sets. The system treats each transition between consecutive data sets as being like or unlike. The like transitions in the sequence are those that the program can process correctly without notifying the system to treat the data set as unlike. For example, you must concatenate data sets with different record formats as unlike unless the data meets the requirements of a different record format. For example, if all the format-V records are the same length, you can specify format-F when reading. If you specify format-U, you can read any format.

If either of the data sets in a transition is system managed, you can treat the transition as like. However, you must ensure that both data sets meet all like concatenation rules, or unpredictable results can occur (for example, OPEN ABENDs).

Your program indicates whether the system is to treat the data sets as like or unlike by setting the bit DCBOFPPC. The DCB macro assembles this bit as 0, which indicates like data sets. See Concatenating Unlike Data Sets.