Determining segment frequency

After you have determined the total size of a segment type, you need to determine segment frequency.

Segment frequency is the average number of occurrences of a particular segment type in the database record. To determine segment frequency, first determine the average number of times a segment occurs under its immediate physical parent.

For example, in the database record in the following figure, the ITEMS segment occurs an average of 10 times for each DEPOSITS segment. The DEPOSITS segment occurs an average of four times for each CUSTOMER root segment. The frequency of a root segment is always one.

Figure 1. Segment sizes and average segment occurrences
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To determine the average number of occurrences of a particular segment type in the database record, multiply together the segment frequencies of each segment in the path from the given segment back up to the root. For the ITEMS segment type, the path includes the ITEMS segment and the DEPOSITS segment. The segment frequency of ITEMS is 10, and the segment frequency of DEPOSITS is 4. Therefore, the average number of occurrences of the ITEMS segment in the database record is 40 (10 x 4). Another way of expressing this idea is that each customer has an average of 4 DEPOSITS, and each DEPOSIT has an average of 10 ITEMS. Therefore, for each customer, an average of 40 (10 x 4) ITEMS exist in the database record.