With relative and indexed files, the dynamic access mode allows you to switch back and forth between sequential access mode and random access mode while reading a file by using the NEXT phrase on the READ statement. NEXT and READ functionalities will be discussed in the next chapter.andom Access. When the access mode is RANDOM, the method of record retrieval changes as per the selected file organization. For indexed files, records are accessed according to the value placed in a key field which can be primary or alternate key. There can be one or more alternate indexes.