Conditions for Using a Network Diagramming Template

Think about building a house when all the pieces are already prepared. You're only responsible for assembling the parts and making minor adjustments. Once you build the first house, you can use the pattern to build others.

Network diagram templates, like prefabricated houses, are standardized, pre-built components. They allow you to use successful past projects as models for the current project and schedule planning activities. Using network diagram templates helps you improve the accuracy of activity sequencing by highlighting successful practices from past projects.

Network diagram templates help you complete your work more quickly because much of the work has already been done for you. Using the successful elements from past projects also saves money on the overall current project.

Finding similarities between past and current projects is extremely helpful in planning and activity sequencing. It is appropriate to use network diagram templates as a tool for activity sequencing, when there are similarities between overall projects and among subprojects in larger projects.

• Similarities between projects - The first situation in which you should consider using network diagram templates as a tool for activity sequencing is when similarities between two separate projects are identified. Some similarities between projects include phases and deliverables. Effective network diagram templates cover the entire project and are especially useful when the past and current projects share a common structure.
  
  Consider the following example. Jack, the training director for a large engineering firm, is responsible for the continued development of in-house training courses. Since each training course has the same design cycle, Jack is able to use network diagram templates for activity sequencing of these internal courses.
  

• Similarities between subprojects - The second situation in which network diagram templates are useful is when there are similar features within a single project. These features are often called subprojects or subnets. Subnet templates are useful for projects where there are several identical features within the work breakdown structure. After completing a network diagram for the first subnet, you can use it as a template for other components within the same project.
  
  It is best to use subnet diagram templates with projects that have repetitive phases, such as floors in a high-rise building, clinical trials in pharmaceutical research, or program modules in a software project.
  

Network diagram templates can help you save time by reducing the duplication of effort where similarities between projects and subprojects exist. Understanding when to use diagramming templates will allow you to reach project goals more quickly an

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Conditional Diagramming Method (CDM)

A third technique for constructing network diagrams is the conditional diagramming method (CDM).

Like other diagramming methods, the CDM uses nodes and arrows to represent the activities and dependencies in a project network. However, this method is distinguishable from other diagramming techniques by its loops and conditional branches.

Loops seen in the CDM indicate the repetition of activities in the activity network.

Conditional branches indicate options in a CDM diagram. The truth or falsity of a condition determines whether contingent activities will happen next.

For example, one phase of auto manufacturing involves painting the auto body. The activities that make up this phase may be outlined in the CDM diagram. In this case, the pass or fail condition of the painted auto body determines whether the auto body is delivered or redone. Delivering the auto body or redoing it are conditional branches or options dependent on the outcome of the pass/fail test.

In project management, the diagramming technique known as Graphical Evaluation and Review Technique (GERT) uses the CDM.

The conditional diagramming method is a technique that represents a network and shows the repeating and conditional activities in the project. This technique is valuable for helping you visualize and plan an activity's schedule. Using the CDM will help you to stay in control of the schedule which, in turn, will increase your chances of a successful project.

Arrow Diagramming Method (ADM)

Every project consists of a number of tasks which must be coordinated and scheduled to meet project goals and deadlines. A project planning network is a graphical representation of the overall project. Its graphical elements indicate activity duration and "precedence relationships," the order in which project tasks must be performed.

Various techniques exist for constructing network diagrams. One popular technique is the arrow diagramming method (ADM). The ADM, also known as the activity-on-arrow (AOA) network, uses arrows to represent activities and nodes to show dependencies.

In the ADM, activities are connected at points called nodes. A node preceding an activity arrow is the start event for that activity. A node following an activity arrow is the end event for that activity.

The ADM uses only finish-to-start (FS) activity dependencies. This means that activity A must finish before activity B can begin.

The first thing to remember when using the ADM is that an activity can't be represented by more than one arrow in the network diagram. Suppose activity A precedes two activities in a network. To avoid duplicating activity A on the diagram, you would need to follow one arrow representing activity A by an end node. Then follow this end node for A by the two successor activities, B and C.

The second thing to remember is that no two activities can have the same begin and end nodes. Instead, if two activities are related or dependent, you can use a "dummy" activity to show the relationship. A dummy uses no resources and is represented by a dashed arrow.

In addition to activities and dependencies, the ADM shows the early and late schedules for the project. Both the early time (TE) and the late time (TL) for an event appear on the event node.

The ADM also allows project managers to specify activity scheduling flexibility by calculating "float." Float is the amount of time available to complete an activity without affecting project duration. To determine a project activity's float, or slack, you would calculate the difference between the activity's late and early schedule times.

Once float has been determined for each event in the network, it is possible to find the critical path through that network. The critical path shows the earliest possible completion time of the entire project. To find the critical path in an AOA network diagram, you would follow the path that connects all events with zero float since activities with a positive float are, of necessity, not on the critical path.

The arrow diagramming method is a method used to construct network diagrams. Arrow diagramming is said to be "event-oriented" because the arrows represent activities. Arrow diagramming reveals the network sequence and timing of activities which is useful in managing the project's schedule.

Precedence Diagramming Method (PDM)

A project is a series of interconnected activities that can be represented by the project network diagram. Various techniques exist for constructing network diagrams. One of the most common is the precedence diagramming method (PDM).

The PDM uses nodes to represent project activities and connecting arrows to show activity dependencies. This technique is also called the activity-on-node (AON) network approach.

To construct a network diagram, you need to consider four types of precedence relationships: finish-to-start (FS), start-to-start (SS), start-to-finish (SF), and finish-to-finish (FF).

• finish-to-start (FS)
  The FS relationship is one in which activity A must finish before activity B can begin. This is the most commonly used type of precedence relationship.
  

• start-to-start (SS)
  The SS relationship is one in which activity A must start before activity B can start. As an example, let activity A be compiling a phone list, and Activity B be calling the people on the list. In this example, compiling the phone list (A) must start before calling the people on the list (B) can start.
  

• start-to-finish (SF)
  The SF relationship is one in which activity A must start before activity B can finish. Let activity A be breathing on one's own. Let activity B be breathing with the aid of a respirator. Breathing on one's own must start (A) before breathing with the aid of a respirator (B) can finish.
  

• finish-to-finish (FF)
  The FF relationship is one in which activity A must finish before activity B can finish. Let activity A be a telemarketing department compiling a phone list. Let activity B be calling the people on the list. Compiling the phone list (A) must finish before calling the people on the list (B) can finish.
  

To convey as much information as clearly as possible, project network diagrams also include early and late schedules.

• the early schedule
  The early schedule is made up of the earliest start (ES) and earliest finish (EF) times. In a project, the ES for an activity is the earliest possible time that the activity can begin. The EF is the earliest possible time that the activity can end.
  
  You can determine the ES for an activity by looking at its predecessors. No predecessors means that the ES is day one, the beginning of the project. One predecessor means that the ES for the activity is dependent on the EF of the predecessor. More than one predecessor means that the ES of the activity depends on the maximum of the EF times of the predecessor activities.
  

• the late schedule
  The late schedule consists of the latest start (LS) and latest finish (LF) times. In a project, the LS and LF are the latest times that an activity can begin and end without causing project delay.
  
  You can calculate the LS and the LF times by using the early schedule. First, set the LF time of the last activity to the EF time of the same activity. Likewise, you can determine the LF time of all immediate predecessor activities by choosing the maximum of the EF times on all predecessor nodes.
  

Once the early and late schedules are in place, you can determine a float for an activity by taking the difference, LF minus EF.

LF - EF = LS - ES

The activity has no float if this number is zero. Float allows for some flexibility in project management and can change as the project progresses.
In a project network diagram, the series of activities that determines the earliest possible completion of the project is called the critical path. The critical path is usually defined as those activities for which float is zero.

To determine the critical path, begin with the first activity in the project. Look at its successors. Compare the successors' float values. Select the one with zero float. This is the second activity on the critical path.

Continue from the second activity on the critical path and compare the float for its successors. Select the activity that has zero float and include it in the critical path.

Continue this process to the final activity for a complete critical path. Ultimately, a project cannot finish any sooner than the time it takes to complete the activities on the critical path.

The PDM represents a project as a network of interrelated activities. The PDM is a way to prepare project activities for scheduling by organizing them in terms of the project's relationships, early and late schedules, float, and critical path. In this way, the PDM allows you to arrive at a realistic, workable project schedule.