What distinguishes a reference property?

A reference property is a feature in modeling that indicates a property whose value is obtained from an external source, rather than being contained wholly within the block itself. The correct choice highlights that a reference property exists outside of the block and is needed for invoking behavior. This external dependence allows the block to interact or relate to other elements or systems, essentially linking the behavior of one block to external resources, data, or functionalities.

In systems modeling, this is crucial because many systems operate on data or conditions that are derived from sources external to their immediate structure. By leveraging reference properties, modelers can create more flexible and dynamic models that appropriately reflect complex interactions in a system. This is in contrast to properties that might represent internal attributes or characteristics that are self-contained within the block itself.

Understanding this distinction helps in effectively using modeling languages and frameworks to represent systems that are interconnected and require external data for their operational behavior.