Problem – Describing a Temporal Restriction of One Entity to Other Entities
The situation often occurs that one entity must come into existence or reach a certain state before action can be taken on another entity. The existence or state of the first entity may prevent another entity from coming into existence. If the second entity is permitted to exist, its transition to a new state may be dependent upon the current state of a controlling entity.
Temporal restrictions can be specified through declaration of existence constraints. These existence constraints are expressed through temporal ranges and points. Temporal comparative operators, such as before, after, and during, are used to express timing requirements.
Example – Team Leader When forming a new project team, an organization stipulates that the team leader must be designated before any other team members are named. This places an existence dependency on team members directed towards the team leader.
|Dependent Entity||Team Member|
A multiple listing organization prohibits price reductions on real estate property if the property is not actively listed. In this example, the dependent entity is allowed to exist, but is restricted from reaching the "processed" state if the state of the listing is not in an "active" status.
|Entity||Real Estate Listing|
|Dependent Entity||Price Reduction|