in project management, the Resource Breakdown Structure (RBS) is a standardized list of personnel resources related by function and arranged in a hierarchical structure. The Resource Breakdown Structure standardizes the Departments personnel resources to facilitate planning and controlling of project work. It defines assignable resources such as personnel, from a functional point of view; it identifies "who" is doing the work. The total resources define the Top Level, and each subsequent level is a subset of the resource category (or level) above it. Each descending (lower) level represents an increasingly detailed description of the resource until small enough to be used in conjunction with the Work Breakdown Structure (WBS) to allow the work to be planned, monitored and controlled. en.wikipedia.org