Network Diagrams

Learning the different network diagram methods is important. These network diagrams will be on the test, and there are several questions concerning this area. The Precedence Diagramming Method (PDM) uses boxes or nodes as activities and arrows as dependencies between the nodes. PDM is also known as Activity On Nodes (AON). Most project management software uses this method (see Figure 10-1). Four different dependency relationship types make up the PDM network:

• Finish-to-start An activity must finish before the next activity begins.

• Finish-to-finish An activity must finish before the next activity can finish.

• Start-to-start An activity must start before the next activity can start.

• Start-to-finish An activity must start before the next activity can finish.

Figure 10-1. Precedence Diagramming Method (PDM).

The finish-to-start dependency is the most common one, and it is used in Microsoft Project. An example of this dependency would be having to finish buying paint before you can begin to paint a room. The painting of the room is dependent on purchasing the paint.

The finish-to-finish dependency occurs when one task must be completed before another task can be completed. For instance, you must finish sanding all the walls before you can finish painting all the walls.

The start-to-start dependency means that you must begin a task before another task begins. An example of this dependency would be that you have to start prepping the walls before you can start painting them.

The start-to-finish dependency occurs when something must be started before finishing another task. This dependency often occurs when you are installing a new phone system. You must start the new phone system running before you can finish with the old system. It is very difficult to get a perfect switch, so you need to have redundant activities to make sure you can still have a working phone system.

Q.	The type of dependency that is used by Microsoft Project is a ________ dependency.
		A.	Start-to-finish
		B.	End-to-end
		C.	Finish-to-start
		D.	Start-to-end

The answer is C. Finish-to-start dependencies are the most common types used in most projects.

Q.	Starting a new computer system before turning the old one off is an example of a ________ dependency.
		A.	Start-to-finish
		B.	End-to-end
		C.	Finish-to-start
		D.	Natural

The answer is A. In this example, you are starting a new system but protecting your organization by leaving the old system going until you are certain that a comfortable switchover can be made.

Arrow Diagramming Method (ADM) uses arrows as activities, and nodes are used to connect and show dependencies. In other words, the lines in between nodes are where you place the task name. Thus this method is also called Activity On Arrows (AOA). Though it's not used much in the real world, you still need to understand the method. The important concepts are that with the PDM method, dummy activities are used to show complete relationships between tasks, and the fact that ADM uses only finish-to-start dependences.

Figure 10-2. Arrow Diagramming Method (ADM).

The next methods allow conditional branches (i.e., ifthenelse condition) and loops (i.e., an activity repeated more than once). Graphical Evaluation and Review Technique (GERT) and System Dynamics are examples of this method. Conditional branches are not used in PDM and ADM.

Network templates are useful to speed up network diagramming. Parts of standardized templates can be used in building project networks for repeatable or identical parts of the network, such as coding several programs in software development or imitation and closing phases of projects. These are called subnets or fragnets.

Q.	Which network diagramming method uses dummy activities?
		A.	PDM
		B.	GERT
		C.	PERT
		D.	ADM

The answer is D. ADM (Arrow Diagramming Method) or activities on arrows uses dummy activities to correctly show all logical relationships.

Q.	PDM is also known as what?
		A.	Activities on nodes
		B.	Activities dependencies
		C.	Activities on arrows
		D.	Activities sequencing

The answer is A. The names of the activities are placed in the boxes on the diagram that are known as nodes.

Q.	PDM stands for:
		A.	Positive Daily Mechanisms
		B.	Process Diagramming Method
		C.	Precedence Daily Management
		D.	Precedence Diagramming Method

The answer is D. This is the most commonly used method.

Q.	Conditional branches can be found in:
		A.	GERT
		B.	PERT
		C.	PDM
		D.	AON

The answer is A. The graphical evaluation and review technique can show conditional branches that reflect what happens if a certain action is taken.

After finishing activity sequencing, you will have a project network diagram. The PMBOK describes project network diagrams as "schematic displays of the project's activities and the logical relationships (dependencies) among them" (PMBOK, p. 135). Most project managers use computers to draw network diagrams, but network diagrams can also be constructed manually. I like to use sticky note pads in some cases so that I can move the activities around on a board and have a visual sense of the relationships.

Network diagrams can contain one or more summary tasks. PMBOK also calls these summary tasks hammocks, meaning that they span the beginning and end of the tasks somewhat like a hammock. Summary tasks are a high-level compilation of the tasks below them. You might have to add to or subdivide your activity list during sequencing to establish the correct relationships. Network diagrams also assess resources and time requirements and tradeoffs, in addition to facilitating "what if" exercises and highlighting critical activities.

Q.	A schematic display of the project's activities and the logical relationships among them is a(n) ________.
		A.	Technically difficult process
		B.	Working schedule
		C.	Project network diagram
		D.	Schedule diagram

The answer is C. This is an output from activity sequencing.

Q.	________ are a high-level compilation of the tasks below them.
		A.	WBS
		B.	Summary tasks
		C.	Schedules
		D.	PDM

The answer is B. The summary tasks do not show detail of all the tasks below them.