A circle or ‘‘bubble’’ in a DFD indicates a system entity or process that changes or transforms data. (Some authors prefer to use squares with rounded corners for this symbol.) In physical DFDs (discussed shortly), the label inside a bubble typically contains the title of the person performing a task—for example, ‘‘cashier.’’ In logical DFDs (also discussed shortly), the label inside the bubble describes a transformation process—for example, ‘‘process cash receipts.’’