Figure 5.5 shows an indexed sequential file of three blocks of data.

The addition of a record to the indexed sequential file can present difficulties, however.

This will be a sequential or indexed-sequential file, in key order, with the actual device address of each record as the data.

The former will tend to require an indexed sequential file on a direct access device.

However, there is often a need to refer to sequential files just to answer one or relatively few enquiries.

This method has been described in Chapter 5 on sequential files (see p. 119).

Note that in some cases sequential files also use this format.

This will mean that the data requires more direct access storage space than a sequential file.

Describe the main areas of an indexed sequential file.

It can sort using just three sequential files rather than the four required by merge sort.