[1] The Resource Breakdown Structure includes, at a minimum, the personnel resources needed for successful completion of a project, and preferably contains all resources on which project funds will be spent, including personnel, tools, machinery, materials, equipment and fees and licenses.
[2] Assignable resources, such as personnel, are typically defined from a functional point of view: "who" is doing the work is identified based on their role within the project, rather than their department or role within the parent companies.
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.
In common practice, only non-expendable (i.e., durable goods) resources are listed in an RBS.
The nomenclature is a numbered, hierarchical list of indented layers, each level adds an additional digit representing.