Sequential File Access
Sequential file access is a mode of file access where storage or retrieval begins at a designated point in the file and continues sequentially through the file. RMS begins accessing records at the start of the file, unless you either specify the starting point explicitly or establish a starting point through a previous operation.
In the sequential access mode, your program issues a series of requests to RMS to retrieve or store succeeding records in a file. Before acting on these requests, RMS checks the file organization to determine how to proceed.
There are limitations imposed by sequential access. When accessing data sequentially, a program can access a previous record only by reopening or rewinding the file, or by switching to a random access mode. Another limitation of sequential access is that you can add records only to the end of the file.
Relative files may be accessed sequentially even if some of the fixed-length file cells are empty (because records were never stored in them or because records were deleted from them). RMS ignores empty cells and sequentially searches for the next occupied cell.
When a program sequentially accesses an indexed file, RMS uses one or more indexes to determine the order in which to process the file records. Because index entries are ordered by key values, an index represents a logical ordering of the records in the file. If you define more than one key for the file, each index associated with a key represents a different logical ordering of the records in the file. Your program can then use the sequential access mode to retrieve records in the logical order represented by any index.