Entry-sequenced data set (ESDS)

An entry-sequenced data set (ESDS) is one in which each record is identified by the address that is assigned to it when the record is first entered into the data set. This address is known as its relative byte address (RBA).

Records are held in an ESDS in the sequence in which they were first loaded into the data set. New records that are added to an ESDS always go after the last record in the data set. You cannot change the length of a record, and you cannot delete a record through the RBA base. The only way to delete a record is through an alternative index. After a record has been stored in an ESDS, its RBA remains constant. The browsing function retrieves the records in the sequence in which they were added to the data set.

You use the RBA option on most file control services commands to specify that the RIDFLD contains the RBA of the record that is to be accessed. An RBA is used to access an ESDS. All file control commands that refer to an ESDS base, and specify a RIDFLD, must specify the RBA option. The commands are:

• READ
• READNEXT
• READPREV
• RESETBR
• STARTBR
• WRITE