The DEAT Business Rule Pattern Language

Russell R. Hurlbut, Ph.D.

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Rule Pattern 10: Aggregation

Problem Describing Aggregate Properties

Trends can be detected over a sufficiently large number of sample cases. Once identified, these trends may be used to take corrective actions. Performance requirements are often stated in terms of such aggregate properties.

Solution

A derived meta-attribute may be defined at the collection level that aggregates one or more attributes of the collection. The type of aggregate function and a threshold are defined in order to detect a condition in which action should be taken.

Example Test Question

In order in guarantee that a test question is fair, each question is evaluated for overall average number of students that answered the question correctly. If this fall below the 50% threshold, the question is thrown out. Furthermore, this average is compared against a frequency distribution of how each of five percentile groups fared on the question. The question is also thrown out if any higher percentile group averaged less than 25% below any lower percentile group. This last part applies the Association and Ordering business rule patterns in order to define the threshold.
Test Question Parameters
Aggregate function type average
Threshold 50% of answers correct

Example Customer Phone Support

An organization's service departments requires that if the average delay for support calls exceeds fifteen minutes that corrective actions be taken, such as shifting telephone operators from another product line.

Customer Phone Support Parameters
Aggregate function type average
Threshold 5 minutes

UML Representation and Related Patterns

The Aggregation business rule pattern is modeled in the UML as a derived attribute of a model element that contains a collection. The Association and Ordering business rule patterns may collaborate with this pattern to define the threshold parameter.

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