Activity Network Diagram (AND): Definition & Example

Instructor: Ronald Price

Ron has held a variety of positions in higher ed and business, including 25+ years as an instructor and 20+ years as a corporate senior manager, and consultant.

An activity network diagram (AND) is a quality management tool used to depict the activities of a project that are either in parallel or in series. This lesson describes the construction and application of an AND.

AND Basics

An AND identifies the activity sequences and dependencies critical to the success of a project. Using an AND, project management is able to identify the sequence of activities that should provide the most efficient time and duration estimate for the completion of a project. An AND depicts the sequencing of the activities, the activities that must be completed before other activities can start (in series), the activities that can be performed at the same time (in parallel), and those activities critical to a project's completion time.

AND Symbols

As a version of an Arrow diagram, arrows connect activities to indicate both sequence and dependency. Because the purpose of an AND is to identify the critical path through a project along with its time requirements, a basic AND doesn't require many symbols. In fact, many ANDs are drawn using only three or four drawing symbols, much like a flowchart. As shown in Figure 1, a rectangle with rounded corners represents an activity, an arrow connecting one activity to another shows sequence, a diamond shaped symbol indicates a binary condition test (true or false, yes or no, etc.), and a rectangular box following and activity indicates a product, result, or data that is being passed to the next activity.

Figure 1. The primary symbols used in activity network diagrams (AND)
The primary symbols used in activity network diagrams (AND)

Other symbols, primarily those of the Unified Modeling Language (UML) or the CPM symbol sets are often included on an AND to provide for a higher level of detail or specification for the activities and their scheduling. There are several diagramming software tools available, each of which typically defines its own version of activity diagrams and the symbol set associated with it.

Creating an AND

Let's say you are tasked with creating an AND for a software application project. The AND is to be used to identify the critical path of the project. Typically, a work breakdown structure (WBS) will have preceded the AND and the project's activities, in either summary or detail, will have been identified. In this case, the activities identified are those common to the System Development Life Cycle (SDLC), which are requirements gathering, requirements analysis, system and user interface design, system development, system testing, and implementation. While each of these activities is typically a major sub-project, for this example, let's assume they are your project's activities. Figure 2 illustrates the sequencing and dependencies of the project's activities.

Figure 2. An example of an simplified activity network diagram (AND)
An example of an AND

The AND shown in Figure 2 is a simplified example of a software development project and its activities. Notice that the activities of this project are mostly in series. This means that an activity must be completed before the next activity can start. However, following Activity C an approval of the system design must be obtained from the stakeholders and project sponsors before Activities D, E, and F can begin. The bar symbol inserted after the approval decision indicates that stakeholder approval directly affects all three of the activities connected to it. After the approval is granted, Activities D, E, and F can all be started at the same time or in parallel.

In addition to its name, each activity symbol could contain other information. In our example, an estimated number of days is given for each activity. However, the information included for the activities could be no more than our example or more detailed information, such as early and late start and end dates, duration in days, or perhaps the program classes, files, or documents associated with each activity, like those found on a UML diagram. The data included on an AND is really up to the project manager or stakeholders and may be any data deemed relevant.

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