A tree diagram is one of the tools and techniques that is used in many contexts as well as project management. It is useful for showing the relationships between objects and their component parts. In projects, it is a good way to portray the organizational breakdown structure (OBS), resource breakdown structure (RBS), risk breakdown structure (also RBS), and work breakdown structure (WBS). In addition to being useful to communicate these structures, it can assist in the processes of decomposing the larger elements of the project into smaller, more manageable units.
In the case of the organizational breakdown structure, the "units" can be organizational units (for example, departments or teams). Other "Org Charts" will show the reporting structure of the people rather than the organizational units. Some diagrams will show both the names of the units and the person in charge of that unit, sometimes giving the person's title as well.
Conventions and terminologyEdit
Tree diagrams have a set of conventions, with many variations.
The units or objects in a tree diagram are shown in shapes, for example, rectangles or ovals. Lines between the objects show the elements that compose them (or the reporting structure). The largest or highest object is the "root". The root is usually placed at the top or left of the chart. Each object is connected to the component objects with lines. The relationship between two connected objects is also called a parent-child relationship. The object that is more closely connected to the root is the "parent" and the one that is the next step away from the root is the "child". The child that has no farther decomposition (or no reporting staff) is also called a "leaf".
Tree diagrams are usually shown with the decomposition going from the top-down (vertically) or left to right (horizontally). Organization charts usually show the head of the organization at the top with the people reporting at each level a row down. Risk breakdown structures frequently use a horizontal structure.