Database Summary of a Summary
When a database which is the result of a summary of another database is again summarized, the minimum and maximum values in the 'second summary' are the high and low values of the base values of the "first summary”.
In the following illustration, the original database was collected on a 15-minute interval for a week. This database is then summarized to an hourly interval. In the resulting database (top, center), there are field values averaged over an hour, and maximum/minimum values which are the high and low points of the 15-minute average data.
If this database is again summarized, the average data of the first summary provides the basis for the resulting database. (Note: we do not take a max of a max or a min of a min). The resulting "second generation" summary (top, right) contains field values that are averaged for the day and max/min values that are the high and low points of the hourly average data.
The data could have been summarized directly from the original database to a 1-day interval. However, the resulting database (lower right) would contain daily averages for the fields and max/min values which are the high and low points of the 15 minute average data.
The maximum and minimum fields can also be used when a database is summarized into SQL and Enscribe databases. New fields are created in the DDL file and the SQL catalog to accommodate them.