UMLR — Location: 19.5 Classifier Descriptions Deployment Specification Attributes P. 711 - Why a multiplicity of [0..1]

An artifact can be located in multiple locations, for example, on a disk and in ROM, and in RAM. Similarly, it could execute partially in ROM and also in RAM. In addition, an executable could reside in multiple places in memory on the same machines, with multiple copies running at once. Also they could assigned to different "cores"