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Problem – Describing a Temporal
Aggregate Property of an Entity
The historical state or performance of an entity may reveal trends. Once identified, these trends may be used to take corrective actions. Performance requirements are often stated in terms of such aggregate properties.
Solution
Historical trends of an entity can be expressed though definitions of a temporal aggregate type (e.g. rates or counts). The history of the entity is considered a collection of prior states. A derived meta-attribute may then be defined at the collection level that aggregates one or more attributes of the collection over a specified period of time. The type of aggregate function and a threshold are defined in order to detect a condition in which action should be taken.
Example – Pension
Estimate
A company policy restricts an employee to a maximum of four requests for pension estimates in a calendar year.
|
Attribute Type |
sum |
|
Unit of measure |
pension estimate requests |
|
Period |
calendar year |
|
Threshold |
4 |
A franchiser requires that a dealer must maintain an average monthly sales volume of over $20,000. If the average for any three-month period drops below $20,000, the dealer is placed on probation.
|
Aggregate Type |
average |
|
Unit of measure |
sales volume |
|
Threshold |
$20,000 |
|
Period |
3 months |
The Temporal Aggregation business rule pattern is modeled in the UML as a derived attribute of a model element that contains a collection of its own states. It shares an affinity with the Aggregation business rule pattern in this respect.
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