Demands

Demands specify requests for specific quantities of products (or services) within specific time constraints, as well as client-dependent priority information. In other words, demands are used for representing customer orders, move requirements and other external demands to the scheduling system. In the transportation domain, demands are requests for the transportation organization to have something (cargo, people) moved from one place to another.

The basic pieces of information a demand contains are:

• Release date and due date establish the overall time bounds for scheduling a demand. A demand cannot be scheduled before its release date; scheduling a demand to complete after its due date is possible but undesirable (it may sometimes be necessary to break the due date constraint to complete a schedule).
• Quantity, specified in domain-specific units, informs the scheduling system of the capacity requirements for a particular demand. The quantity will ultimately translate to amount of available capacity being allocated on those resources which execute the schedule generated for the demand.
• Other domain-specific data possibly contained in a demand are information about the requested product (in the transportation world, this would be the type of cargo being transported, its packaging etc.), priority, and additional constraints necessary for the successful scheduling of the demand.

In short, demands are a summary of what the underlying system is expected to produce. As an abstraction, demands map requests into sets of constraints.