Drawing the AON network Project Management lecture Elements

Drawing the AON network Project Management (lecture)

Elements of an Ao. N diagram • Activity (node) – Work element or task – Name or identification of the tasks must be added – No need for dummy (unreal) activities • Dependency or sequence arrow – Shows the interrelationship between activities

Conventions • Time flows from left to right – Arrows’ direction – Labels’ increase • Head nodes always have a greater/higher label (letter) that of the tail node. • A complete network has only one starting and only one ending event.

Examples of activity combinations

Graphical representation • Representation of dependency time: lags • Activity duration times & finish to start dependency • Representation of milestones/deadlines (external constraints): Identified by an inverted triangle over the activity node (occasionally with an imposed time for the event)

Overlapping activities • If the activities are not fully discrete • The second activity can start before the first is completed but not before it is at least partly completed. • Breaking activities into components

Interfacing • When an activity is common to two or more subnetworks it is said to be an ‘interface’ activity between those subnetworks and is represented by a pair of concentric circles or rectangles.

Two errors in logic • Looping: underlying logic must be at fault • Dangling: an activity is undertaken with no result

Hammock activities • Artificial activities created for the representation of the overhead cost with the aim of cost control. • Embrace activities belong to the same cost centre • Zero duration time (not taking part in the time analysis) • Overhead cost rate is assumed to be constant over the life of the hammock.

Multiple starts and finishes • Only used in computer programs • All starting activities can occur at the start and all finish activities will occur at the end of the project.

CPA, CPM and PERT • Critical Path Analysis (CPA), Critical Path Method (CPM) – deterministic with only one estimation • Program Evaluation and Review Technique (PERT) – probabilistic with three estimated durations

Readings • Lockyer – Gordon (2005) Chapter 12

Thanks for the attention!