What is a tree diagram, where is it used and which rules apply?
Visualise the structure of dependent elements
A tree diagram is a graphical representation that displays hierarchical dependencies between individual elements of a network. The name is derived from the appearance of the diagram, which is reminiscent of a tree (turned upside down or lying on its side) with a branched structure. The advantage lies in the simplicity of the representation, the traceability of the dependencies and the clarity of the presented information.
Tree diagrams – alternatively also known as tree graphs or branch diagrams – are used in a wide variety of areas, e.g. as
- family tree,
- cladogram for displaying the relationship of different living beings,
- in mathematics in the visualisation of (multi-level) random experiments and probability calculations,
- phrase structure diagram for structuring texts,
- organisation chart for business organisations,
- decision tree.
According to PMBOK and DIN 69901, the work breakdown structure should be displayed in the form of a tree diagram. In project management, the diagram is also used to represent costs, resources or project organizations.
A special form of the tree diagram is the mind map, which is well suited for the representation of complex connections, but also allows cross connections – in the sense of associations.
Elements and Rules for the Tree Diagram
The following elements and rules apply to the display:
- There is a start node (the root of the tree). The start node is at the top structure level. Visually this means that a tree diagram is built from the start node (in the western project world) from top to bottom or from left to right.
- Each node can branch to any number of nodes in exactly the structure level below it. With the exception of the start node, each node can have exactly one connection in the hierarchy to the top or to the structure level above it.
- The structure levels do not overlap and have no common nodes.
Examples of tree diagrams
Here are four examples of tree diagrams:
- an organisational chart,
- a work breakdown structure,
- amulti-level random experiment,
- and a decision tree.