This is the process, where values from the records in the database, that correspond to a particular node, are totalled, averaged or otherwise processed. These aggregation values are then stored along with other details of that node.

Each aggregation field is given an aggregation name, which defines the name to be used, an aggregation type, which defines the calculation and any extra data such as the fields to be totalled or averaged.

Aggregations fall into several main categories.

• The first contains the simple aggregations, such as totals and averages.

  Take the example of calculating the Average Prize Money won for each node in the Prize Money example. Here, the field, Race Value, will be averaged and stored as an aggregate, on each node in a new field, Average Won.

  More complex aggregations take a group of consecutive fields in the database records and summarise them to a node. Both totalling and averaging are possible.

• Another group counts the number of fields that match specific criteria. These can be expressed as simple counts or percentages.

• Others perform arithmetic on previous aggregation fields or copy data from the database records.

See Aggregation in Appendix B of the Daisy Manual for more details.