Figure 1 illustrates the structure of an alternate index connected to an entry-sequenced data set. The salesman's name is the alternate key in this example.

Figure 1. Alternate Index Structure for an Entry-Sequenced Data Set

If you ask to access records with the alternate key of BEN, VSAM does the following:

1. VSAM scans the index component of the alternate index, looking for a value greater than or equal to BEN.
2. The entry FRED points VSAM to a data control interval in the alternate index.
3. VSAM scans the alternate index data control interval looking for an entry that matches the search argument, BEN.
4. When located, the entry BEN has an associated pointer, 400, that points to an RBA in the base cluster.
5. VSAM retrieves the record with an RBA of X'400' from the base cluster.