An aggregation attribute allows data related to a record to be aggregated and treated as if a field within that record.
For example, assume that we have a customer table, and a related order table. Order is related to customer – a single customer, with a record in the customer table, may have several orders, each of which is represented by a record in the order table. An aggregation attribute can be used to aggregate the customer’s order data against the customer record – a ‘Number of orders’ attribute could be created to count the number of orders placed by each customer. Equally, a ‘Total orders value’ or ‘Average order value’ attribute could be created.