A Relative Record Data Set (RRDS) is a type of data set used by the VSAM computer data storage system. Records are accessed based on their ordinal position in the file (relative record number, RRN). For example, the desired record to be accessed might be the 42nd record in the file out of 999 total.
The concept of RRDS is similar to sequential access method, but it can access with data in random access and dynamic access.
Physical structure of RRDS is described that it has data record in sequence. Its logical structure follows Physical one of it. One record stands after Previous records like some people stand in line. The record exists in turn of number called relative record number indicates logical positional relativity in the file. Operator can realize the function of randaom access and dynamic access by designating this relative number. Consequently, when You do reading or writing of record, you must know where the record you want in file is. Calling of Relative Record Data Set includes that doing random access by naming relative record by will or doing sequential access by naming the number in turn from the relative record number you indicate. Consequently, RRDS has the same function as Key Sequenced Data Set
in the way of data set calling. The difference from Key Sequenced Data Set is that RRDS has no any keys.