Purpose

To control Date Alias Instances resulting from a Date Alias Offset relationship such that the Date Alias Instance cannot fall on certain specified days

This form is accessed via a button in the Maintain Date Aliases form (CALF0420). In that form, a Date Alias is able to be defined in terms of an offset from another Date Alias. When an instance of the first Date Alias is created, the date of the second is calculated as the first date plus or minus the offset.

This form is used (optionally) to ensure that the calculation of the second date results in that date falling on 'acceptable' days. For example, the second date can be constrained to fall outside Institution holidays or only on a weekday or only on a Wednesday (or any valid combination of any of the constraints).

With constraints defined, when an instance of the first Date Alias is created, the date of the second is calculated as the first date plus the offset. If this falls either on a day specified by a constraint as unacceptable or doesn't fall on a day specified as the required day, the date is moved forward or backward until the constraint is satisfied. For example, if the calculated date of the second Date Alias falls on a Saturday, and the constraint WEEKDAY,MUST,1 (i.e. Date Alias Instance must fall between Monday and Friday inclusive) has been specified for the Date Alias, the instance is moved forward to Monday in order to satisfy the constraint. Monday's date forms the Date Alias instance.

In each case a number of resolution days must be specified. If the calculated date falls on a day which conflicts with the recorded constraints, the System moves the calculated date forward or backward that number of days. For example, if resolution days is set to 2, and the constraint MONDAY, MUST NOT is set, and the date calculated from the offset falls on a Monday, the date is moved forward two days to Wednesday.

This form is accessed through CALF0420, via the Offset Contraints button (2nd block) .

The Date Alias Offset block contains:

• Date Alias
• Offset Date Alias

The Date Alias Offset Contraint block contains:

• System Date Offset Contraint Type 
  This parameter defines the day or days used in the constraint. E.g. MONDAY, WEEKDAY, HOLIDAY.
• Description
• Condition
  This parameter is the operator which acts on the constraint type. The available conditions are MUST and MUST NOT.
  For example, MUST (be a) MONDAY; MUST (be a) WEEKDAY; MUST NOT (be a) HOLIDAY
• Resolution Days
  This is the number of days which a calculated date should be moved forward or backward in order to resolve a constraint.
  For example, 3 moves a calculated date forward from Monday to Thursday (provided no other constraint prevents this)

  Button

  • Back

Notes/Rules:

Date Alias instances based on HOLIDAY calendars can only have absolute values. i.e. cannot be offset values and hence cannot be subject to offset constraints.

The System constraint type HOLIDAY recognises any single date in a Holiday calendar (a calendar of calendar category HOLIDAY). The System constraint type INST BREAK recognises Date Alias pairs in Holiday calendars (the paired Date Alias Instances need not be in the same Calendar Instance.

For example, the holiday could have a start-break in 2002 holiday calendar and end-break in the 2003 holiday calendar) as a Date Range. The constraint uses all days within the range.

The user is warned of an unresolvable constraint either when the constraint is recorded (for more common conflicts) or when Date Alias Instances are being created using offsets. If the system is unable to resolve the constraint/s at the point of deriving the alias value, it ignores the constraints and calculates the alias value from the offset Date Alias Instance.