PERT chart - Project management plan

"A project network is a graph (flow chart) depicting the sequence in which a project's terminal elements are to be completed by showing terminal elements and their dependencies.
... the project network shows the "before-after" relations.
The most popular form of project network is activity on node, the other one is activity on arrow.
The condition for a valid project network is that it doesn't contain any circular references." [Project network. Wikipedia]
The PERT chart example "Project management plan" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the solution "Seven Management and Planning Tools" from the Management area of ConceptDraw Solution Park.