6.1.2.4 Indexed Sequential Access Methods

Indexed Sequential Access Methods are a way of arranging database information so that records can be accessed both by key and by key sequence (ordering). ISAM is not part of Codd’s relational model.

Associative memory in B-Trees is an example of a database implementation which can support a native key ordering. SLIB’s alist-table implementation uses sort to implement for-each-row-in-order, but does not support isam-next and isam-prev.

The multi-primary-key ordering employed by these operations is the lexicographic collation of those primary-key fields in their given order. For example:

(12 a 34) < (12 a 36) < (12 b 1) < (13 a 0)