Depending on the context in which it is used, the term resource can have many different meanings. The dictionary defines a resource as a source of supply, support, or aid that can be readily drawn on when needed. Examples of resources include a laborer used to assemble a machine, an operating room required by a patient, or a truck needed to transport supplies. In some simulation packages, a resource is considered a supply of items; in other simulation packages, resources are entities that provide a service to other items in the simulation model. In some models the available resources might be unlimited, while in other models the number of units of a resource might be limited, or fixed. The number of available resource units can vary throughout a simulation run and can be governed by a schedule. The availability of resources can affect the flow of entities during a simulation run.

In Simulation Studio, resources are special objects that provide services or materials to entities. Often the availability of resources facilitates the flow of other entities in the system during the simulation, and a shortage of resources could restrain the flow of these entities.

Systems modeled in Simulation Studio can use two kinds of resource objects: stationary resources and mobile resources. Some entity holding blocks (such as the Queue, Server, and Delay blocks) represent stationary resources in a simulation model. These are static and created at model building time. Mobile resources, which are dynamic and created during the experimental run of the simulation model, are the resource objects that flow in the model. Mobile resources are defined as a special type of entity and possess all the capability and attributes of regular entities. They can be processed and managed by the facilities and blocks for the regular entity objects in many parts of a simulation model. The resource entity and related subjects are the main focus of this chapter. Unless stated otherwise, the term resource refers to a resource entity.

Like other entities, resource entities are objects that can carry attributes. All resource entities in Simulation Studio have a predefined entity attribute named ResourceUnits which represents the capacity, or number of units, of the resource. While the ResourceUnits attribute has special uses for resource entities, it can also be used as an ordinary numeric entity attribute for modeling purposes. In addition to the ResourceUnits attribute, each resource entity also has run-time state information (such as resource state and seizing status) that is used by the simulation system to perform resource management during the run. From a user’s point of view, the resource state can be either Functional or Nonfunctional (such as Failed, Maintenance, or Offline).