We have seen how anything that can change over time is potentially a timeline aware rule. Existence timelines allow you to specify the dates that a rule can exist as well as what value to use before, during and after these dates. An existence timeline creates a timeline of a specified type from a pair of inclusive start and end dates, either of which is optional.
- Create a new rule called "Student Grants Amount" and set its type to Number. From the palette on the right-hand side of the editor, drag an existencetimeline element onto the rule element on the diagram. Change the name of the existencetimeline to be "Student Grants Amount".
- View the diagram in technical view. See the CER Editor Layout.
- Drag a Date from the palette to the start date for the existencetimeline. Repeat this step for the end date.
- Set the dates to be the date a person started college and the date a person finished college.
- Drag a Number from the palette to the before, during and after date ranges.
- Set the "Value Before Date Range" to be 0. This means the value of the grant before the person started college evaluates to 0.
- Set the "Value During Date Range" to be 1000. This means the value of the grant during the period the person attended college evaluates to 1000.
- Set the "Value After Date Range" to be 200. This means the value of the grant after the person finished college evaluates to 200.