Simulation Studio implements an object named entity group that is a collection of entity references. An entity reference contains information that uniquely identifies a particular entity. Therefore, an entity group holds information about a collection of entities, but not the actual entities themselves. Entity groups add another level of modeling sophistication to your simulation modeling environment.
Most holding-type blocks, such as the Queue, Server, and Delay blocks, provide an OutHoldings output port that you can use to pull an entity group that contains references to the entities currently held by the block. Other Simulation Studio blocks can use this information to inspect the contents of a holding block and then act on that information, possibly preempting specific entities from the holding block. Some blocks (the Queue and Server blocks, for example) have an InPreempt input port that accepts an entity group as input. These blocks compare the entity references in the incoming entity group to the entities currently being held by the block and preempt any matches.
The Entity Group Holder block can be used to create a new entity group (with characteristics specific to your model needs) that can then be used by other blocks in your model. The Gate and Seize blocks also make use of entity groups. See Appendix A: Templates, for details about these and other blocks that use entity group objects.