Project Network & Network Analysis

Princess C. AssistinDennis A. Alonzo

- Project Network -

• A project network is a graph (flow chart) depicting the sequence in which a project's terminal elements are to be completed by showing terminal elements and their dependencies. It is always drawn from left to right to reflect project chronology.

Project Network (fig.)

Project Network• The work breakdown structure or the product breakdown

structure show the "part-whole" relations. In contrast, the project network shows the "before-after" relations.

• The most popular form of project network is activity on node (AON)(as shown in the figure), the other one is activity on arrow (AOA).

• The condition for a valid project network is that it doesn't contain any circular references.

• Project dependencies can also be depicted by a predecessor table. Although such a form is very inconvenient for human analysis, project management software often offers such a view for data entry.

• An alternative way of showing and analyzing the sequence of project work is the design structure matrix.

Most Popular Form of Project Network

Activity on Node (AON)

Activity on Arrow (AOA)

Activity on Node

Activity-on-node is a project management term that refers to a precedence diagramming method which uses boxes to denote schedule activities. These various boxes or “nodes” are connected from beginning to end with arrows to depict a logical progression of the dependencies between the schedule activities.

Activity on Node (cont.)

Each node is coded with a letter or number that correlates to an activity on the project schedule. Typically, an activity-on-node diagram will be designed to show which activities must be completed in order for other activities to commence. This is referred to as “finish-to-start” precedence – meaning one activity must be finished before the next one can start. In the diagram below, activities A and D must be done so that activity E can begin. It is also possible to create other variations of this type of diagram. For example, a “start-to-start” diagram is one in which a predecessor activity must simply be started rather than fully completed in order for the successor activity to be initiated.

Activity on Node - DiagramAn activity-on-

node diagram can be used to provide a visual representation of the logic of an entire project schedule. Or, it can be used for any smaller section of the schedule that lends itself to being represented as having a defined beginning and end. To keep the logic in the diagram simple, it may be most effective to include only critical path schedule activities. The planned start date of each node may also be listed in the diagram legend in accordance with the project management timeline.

Activity on ArrowArrow diagramming

method (ADM) is a network diagramming technique in which activities are represented by arrows. ADM is also known as the activity-on-arrow (AOA) method.

ADM is used for scheduling activities in a project plan. Precedence relationships between activities are represented by circles connected by one or more arrows. The length of the arrow represents the duration of the relevant activity. ADM only shows finish-to-start relationships, meaning that each activity is completed before the successor activity starts.

Sometimes a "dummy task" is added, to represent a dependency between tasks, which does not represent any actual activity. The dummy task is added to indicate precedence that can't be expressed using only the actual activities. Such a dummy task often has a completion time of 0.

Network Analysis Network analysis is the general name given to certain specific techniques which can be used for the planning, management and control of projects. One definition of a project (from the Project Management Institute) is

A project is a temporary endeavour undertaken to create a "unique" product or service

This definition serves to highlight some essential features of a project

• it is temporary - it has a beginning and an end• it is "unique" in some way

Network Analysis (cont.)Typically all projects can be broken down into:

• separate activities (tasks/jobs) - where each activity has an associated duration or completion time (i.e. the time from the start of the activity to its finish)

• precedence relationships - which govern the order in which we may perform the activities, e.g. in a project concerned with building a house the activity "erect all four walls" must be finished before the activity "put roof on" can start

and the problem is to bring all these activities together in a coherent fashion to complete the project.

Network Analysis (cont.)Two different techniques for network

analysis were developed independently in the late 1950's - these were:

• PERT (for Program Evaluation and Review Technique); and

• CPM (for Critical Path Management).

PERTPERT was developed to aid the US Navy in the planning and control of its Polaris missile program . This was a project to build a strategic weapons system, namely the first submarine launched intercontinental ballistic missile, at the time of the Cold War between the USA and Russia. Military doctrine at that time emphasised 'MAD - mutually assured destruction', namely if the other side struck first then sufficient nuclear weapons would remain to obliterate their homeland. That way peace was preserved. By the late 1950s the USA believed (or more importantly believed that the Russians believed) that American land based missiles and nuclear bombers were vulnerable to a first strike.

PERT (cont.)

Hence there was a strategic emphasis on completing the Polaris project as quickly as possible, cost was not an issue. However no one had ever build a submarine launched intercontinental ballistic missile before, so dealing with uncertainty was a key issue. PERT has the ability to cope with uncertain activity completion times (e.g. for a particular activity the most likely completion time is 4 weeks but it could be any time between 3 weeks and 8 weeks).

CPM

CPM was developed in the 1950's as a result of a joint effort by the DuPont Company and Remington Rand Univac. As these were commercial companies cost was an issue, unlike the Polaris project mentioned above. In CPM the emphasis is on the trade-off between the cost of the project and its overall completion time (e.g. for certain activities it may be possible to decrease their completion times by spending more money - how does this affect the overall completion time of the project?)

PERT/CPMModern commercial software packages tend to blur the distinction between PERT and CPM and include options for uncertain activity completion times and project completion time/project cost trade-off analysis. Note here that many such packages exist for doing network analysis.

There is no clear terminology in the literature and you will see this area referred to by the phrases: network analysis, PERT, CPM, PERT/CPM, critical path analysis and project planning.

Network analysis is a vital technique in PROJECT MANAGEMENT. It enables us to take a systematic quantitative structured approach to the problem of managing a project through to successful completion. Moreover, as will become clear below, it has a graphical representation which means it can be understood and used by those with a less technical background.

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