The physical placement of record occurrences on pages is independent of set relationships. Set relationships are implemented in the database using db-keys as pointers. Each record in a chain set has a four byte binary pointer in its prefix whose value is the page and line number (the db-key) of the next record in the set.
For example, the owner and member records of the DEPT-EMPLOYEE set for MIS are located on four non-contiguous pages, as illustrated in the following figure.
Although the records are not stored next to each other, it is possible to determine the logical structure of the MIS set occurrence by following the pointers. The next pointer for Peter Plum is 3888/2. Sandy Shore is located on page 3888, line 2 so she is the NEXT record in the DEPT-EMPLOYEE set for MIS. The next pointer for Sandy Shore is 2525/3 which leads to John Done's record occurrence. John follows Sandy in the DEPT-EMPLOYEE set.
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