A dummy activity is a simulated activity of sorts, one that is of a zero duration and is created for the sole purpose of demonstrating a specific relationship and path of action on the arrow diagramming method. Dummy activities are a useful tool to implement when the specific logical relationship between two particular activities on the arrow diagramming method cannot specifically be linked or conceptualized through simple use of arrows going from one activity to another. In this case, the creation of a dummy activity, which serves essentially as a form of a placeholder, can provide exceedingly valuable. Dummy activities should in no cases be allocated any duration of time in the planning and/or scheduling or project activities and components. When they are illustrated in a graphical format, dummy activities should be represented by the user of a dashed line with an arrow head on one end, and may in some cases be represented by a unique color.
Dummy Activities in Scheduling Network Diagrams Dummy activities are used in Activity on Arrow (AOA) diagrams, a type of scheduling network diagram, to represent dependencies or logical relationships without consuming any time or resources. These activities are represented as dashed arrows in the network diagram. Dummy activities are primarily used to: Maintain the logical relationships between activities. Avoid ambiguity in the diagram. Ensure that each activity has a unique identifier and dependency path. Examples of Dummy Activities in HTML Example 1: Shared Dependencies
Shared Dependencies
Scenario: Activity A and Activity B are predecessors of Activity D. Activity C is a predecessor of Activity B and Activity D.
Diagram:
A ----> D1 (dummy) ----> D
C -------------> B ----> D
Example 2: Diverging Paths
Diverging Paths
Scenario: Activity A splits into two paths:
- Path 1: A → B → D
- Path 2: A → C → D
Issue: Directly connecting A to D could cause confusion about which path is responsible.
Diagram:
A ----> B ----> D
\ \
C ----> D1 (dummy) ----> D
Example 3: Sequential Logic
Sequential Logic
Scenario: Activities B and C both follow Activity A, but they need to be completed before Activity D starts.
Issue: It may not be clear in the diagram that both B and C are required.
Diagram:
A ----> B ----> D1 (dummy) ----> D
\ /
C ------/
Example 4: House Construction Example
House Construction Example
Scenario: Consider a project to build a house with the following activities:
- A: Lay foundation.
- B: Install plumbing.
- C: Construct walls.
- D: Install electrical systems (dependent on plumbing and walls).
Issue: D depends on B and C, but there is no direct relationship between A and D.
Diagram:
A ----> B ----> D
\
C ----> D1 (dummy) ----> D