MyDrawA Hierarchy Chart (hierarchical diagram) shows the breakdown of a system to its lowest manageable parts. It is a top-down modular design tool, constructed of rectangles (that represents the different modules in a system) and lines that connect them. The lines explain the connection and/or ownership between the different modules among the system just like in an organizational chart.
Those diagrams are used to present all parts in a system and the way they are arranged in it. A hierarchy chart starts with the name of the system as a single entity and through a drill-down list all different parts of this entity. It is used for describing the structure of a whole along with all its parts which are small enough to be understood by a human brain.