Resources
A resource, in the context of STK Scheduler, is a virtual entity that represents a real-word object or constraining property of an object. A resource may be a person, a vehicle, a computer, an area to image, etc. Anything that is required to accomplish a task may be considered a resource. To accomplish the task of baking a cake, for instance, one needs a cake, an oven, gas or electricity, heat, and time. All of these are resources. Time is a special resource in scheduling problems. Because all tasks require time and time can be defined in a universal manner for all tasks, a time resource need not be created (See Time in STK Scheduler). All of the other resources: cake, an oven, gas or electricity, and heat, may be defined as resources in STK Scheduler.
Modeling a Real-world Problem
Resources provide constraints to a task. The number of resources required for any given task will change depending on the complexity of the problem and on the fidelity by which you want to model the problem. Let's say, for instance, that the oven in the above example uses electricity as its power source. If your house is located on an island you may use a diesel generator to create your electricity. In this case you may want to include diesel fuel as a resource. If, however, your house us in the middle of a sun-bathed dessert you may use solar energy to create your electricity. In such a case, solar energy may be considered a free and unlimited source of power, so electricity is not really a constraint on the baking task and may be removed completely (Of course since you cannot bake at night, you may want to include a sunlight resource). Then again, if you are like most people, we just pay for the electricity we use, so we could add money as a resource. If we wanted to increase the complexity, we could add a baker as a resource. We could get a bit carried away and add food for the baker to eat, water for him to drink, light for him to see by etc. It is doubtful that such details are necessary to solve a simple scheduling problem such as baking a cake, but there is nothing in STK Scheduler that will limit modeling to this degree.
The more complex a scheduling problem is, the more ways it may be modeled through the use of resources. It is important to match the scope of your resource modeling to your scheduling needs. When defining a scheduling problem, resources should be defined prior to tasks. This ensures that the resource exists when it is time to define a task's resource constraints. Of course if the need arises, a resource may be defined at anytime, and a task's resource constraints may be altered to include a resource at anytime (as long as that resource exists).
Defining Resources and Resource Attributes
All resource have properties that limit their usefulness. Since resources are required to accomplish tasks, the limitations of a resource will limit the way tasks can use them. Resources are defined by a series of attributes that ultimately define the limitations they impose. All of a resource's attributes are contained within the Resource Definition Form. This form can be used to define new resources as well as to modify existing resources.
