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BASIC RULES TO FOLLOW IN THE DEVELOPMENT OF PROJECT NETWORKS

Class notes on the development of the network for the project, the con...
Course

 Project Management (ADMG 374 )

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Students shared 15 documents in this course
Academic year: 2020/2021
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Patrick Gomez
Central Washington University
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BASIC RULES TO FOLLOW IN THE DEVELOPMENT OF PROJECT NETWORKS

The following eight rules apply broadly when a project network is being developed.

  1. Networks usually flow from left to right.
  2. An activity cannot begin until all connected preceding activities have been completed.
  3. Arrows in networks point to precedence and flow. They can also cross each other.
  4. Each activity must have a unique identification number.
  5. The activity identification number must be greater than that of the activity preceding it.
  6. Closed circuits are not allowed (in other words, no recycling should be done through a set of activities).
  7. Conditional assertions are not allowed (i. such assertions should not appear. If successful, do something, other than do nothing).)
  8. Experience suggests that when there are many beginnings, a common startup node can be used to clearly indicate where the project will start on the network. It is also possible to use a single end of the project to indicate an end clearly.

Node Activity Basics (AEN)

The high availability of personal computers and graphics programs has served as an impetus to use the node activity method (AEN, sometimes referred to as the precedence diagram method). An activity is represented by a node (box). This one can take many forms, but in recent years it has been depicted more than anything as a rectangle (box). Dependencies between activities are represented by arrows between rectangles (boxes) in the AEN network.

Arrows indicate how activities relate and the sequence in which things should be accomplished. The length and slope of the arrow are arbitrary and are set for convenience to draw the net. The letters on the boxes are used to identify activities while learning the basics of building and analyzing networks. In practice, activities have identification numbers and descriptions. There are three basic relationships that need to be established for activities that are included in a project network. Relationships can be determined after answering the following three questions for each of the activities:

  1. What activities should be completed immediately prior to this activity? These are called ancestor activities.

  2. What activities should you follow immediately to this activity? These are called successor activities.

  3. What activities can occur while this activity is taking place? This is known as a concurrent or parallel relationship.

Sometimes the administrator can only use the first and third questions to establish relationships. This information allows the network analyst to construct a graphical flowchart of the sequence and logical interdependence of project activities.

ActivitiesY and Z cannot begin until activity X is complete. ActivitiesY and Z can occur at the same time, or in parallel, if the project manager so desires; however, this is not a necessary condition. For example, emptying a concrete street (activity Y) can occur while gardening (activity Z), but land cleanup (activity X) must be completed before activities Y and Z can begin. These two are considered parallel activities. As such, they allow for concurrent efforts that can shorten the time to perform a number of activities. Sometimes the X is called explosive activity, since more than one arrow leaves the node. The number of arrows indicates how many activities immediately follow activity X.

Activities J, K, and L, which can occur at the same time if desired, and activity M, which cannot begin until J, K, and L are finished. The latter are parallel activities. M is called a merge activity because more than one activity must be terminated before M can begin. Activity M can also be called an important fact. TheX and Y activities are parallel, i. they can occur at the same time; the Z and AA activities are also parallel. But the latter two cannot begin until those two conclude.

Given these AEN fundamentals, we can practice developing a simple network. Remember, arrows can cross over each other, they can bend, or have any length or slope. Cleaning is not a criterion for a valid and useful network, only the precise inclusion of all project activities, their dependence and time estimates. This project represents a new business center to be developed, and the work and services that the county's engineering design department must provide as it coordinates with other groups, such as business center owners and contractors.

It is noted that activity A (approval of the application) has no precedent; therefore, it is the first node to draw. We then warn that activities B, C and D (construction plans, traffic analysis and service availability verification) are preceded by activity A. We draw three arrows and connect them to activities B, C and D. This segment shows the project administrator that activity A must complete before B, C, and D can begin. B, C, and D can continue concurrently after A ends, if desired.

At this time our project network presents us with a graphical map of the project's activities with sequences and dependencies. This information is too valuable for those who manage the project. However, calculating the duration of each activity will further increase the network value. A realistic project plan and program require reliable time estimates for project activities. The sum of time to the network allows us to calculate how long the project will take. When activities can or should begin, when resources should be available, what activities can be delayed, and when the

(ET) of the last project activity (or, in the case of multiple completion activities, the activity with the longest IT). In some cases there is a deadline imposed for the duration of the project and it will be used. Suppose, for planning purposes, that we can accept that the duration of the TT (TE) project is equal to 235 business days. Activity H FT becomes 235 business days (TT – FT).

Ct for E and G becomes 185 (200 – 15) and 30 business days (200 – 170 x 30), respectively. Then the CT for activity G becomes the FT for activity F and its CT becomes 20. Right now we see that B and C are explosive activities that relate to E and F. The late end for B is controlled by the CT of activities E and F. CT of E is 185 days and 20 days for F. Follow the back arrows from activities E and F to B. Notice that CT times for E and F have been placed to the right of the node so that you can select the smallest time; i. 20 days. The later B can finish is in 20 days, or activity F will be delayed and therefore the entire project. Activity C CT is identical to B because it is also controlled by the CT of activities E and F. Activity D only collects your CT from activity F. By calculating the CT (FT – Dur CT) of B, C and D, we can determine the FT for A, which is an explosive activity. You notice that the end of A is controlled by activity B, which has the smallest FT of B, C and D. As the CT for activity B is period 5, the FT for A is 5 and its time is zero. The backward pass is over and the later times of the activities are known.

Determination of slack time (or flotation)

Once the forward and backward passes have been calculated, it is possible to determine which activities may be delayed by using "slack time" or "float". For an activity, this is simply the difference between CT and IT (CT – IT – TI), or between FT and TT (FT – TT – TI). For example, the slack for C is five days, for D is 10 days, for G it is zero. Total slack time tells us how much time an activity can be delayed without delaying the project. Using the slack time of an activity on a route will delay IT for all activities that follow in the chain and reduce its slack time. The use of all slack time should be coordinated with participants who remain in the chain.

Once the lethargy time of each activity has been calculated, the critical path is easy to identify. When the FT is TT for the final activity of the project, it can be identified to the critical route as to the activities for which FT TT also, or that have a slack time equal to zero (FT – TT - 0 or CT – IT - 0). The critical path is the route(s) of the network that has the shortest clearance time in common. This strange word arrangement is necessary because problems arise when the project completion activity has an FT other than the TT of the last project activity. For example, if the project FT is 235 days, but the imposed TT or target date has been set to 220 days, all activities on the critical route would have a slack time of less than 15 days. Of course, this would result in an early start (15 days for the first project activity), which is a good trick if the project is to start now. A negative slack time occurs in practice when the critical path is delayed.

Delaying any of these activities will take the entire project the same number of days. Critical activities typically account for about 10 percent of project activities. Therefore, project managers pay close attention to critical path activities to ensure that they are not delayed.

We use the term sensitivity to reflect the probability that the original critical path will be modified once the project begins. Sensitivity is a function of the number of critical or near-critical routes. A network program that contains only one critical path and many non-critical activities, with a lot of slack time, might be considered insensitive. Conversely, a sensitive network is one where one or more of the critical routes and/or non-critical activities have very little slack time. Under such circumstances, the original critical path is more likely to change when project work begins.

How sensitive is the Koll Business Center program? Not much since there is only one critical route and each of the non-critical activities has a lot of lethargy time when compared to the estimated duration. Project administrators value the sensitivity of their network programs to determine how much attention they should devote to managing the critical path.

Free slack (float)

Free slack is unique. This is the amount of time that it is possible to delay an activity without delaying the successor activities connected to it. It can never be negative. Only activities presented at the end of a chain of activities (usually when you have a merge activity) can have free slack. For example, if a single chain (path) of activities is only 14 days wide, the last activity will have free space but the others will not. Sometimes the string is not very long; can be single-activity. For example, in the Knoll Business Center network, activity E is a chain of one and has a free space of 165 business days (200 – 35 x 165). Activities C and D also have a free space of five and 10 days, respectively.

The beauty of free slack is that changes in start and end times for free space activity require less coordination with the other project participants and give the project manager greater flexibility than total inactivity. Because the activity is the last in the chain, delaying the activity to the maximum slack time will have no effect on the activities that follow it. For example, suppose a chain of 10 activities. The delay of any of the other nine in the chain requires managers to be notified of the remaining activities in the chain for which there will be delays, so that they can adjust their programs because they do not have slack time.

Using forward and backward pass information

For the project administrator, what does a slack time of 10 business days mean for activity D (service verification)? In this specific case it means that D may be delayed by 10 days. In a broader sense, the project manager soon learns that

Another rule that expires to the project network and the calculation process is the establishment of circuits. It's an attempt by the glider to return to a previous activity. Remember that activity identification numbers must always be higher for activities that follow a particular activity; this rule helps avoid the illogical relationships of precedence between activities. An activity should occur only once; if repeated, it must have a new name and identification number and must be placed in the right sequence on the network. If it were allowed to exist, the route would repeat itself perpetually. Many computer programs detect this type of logical error.

Numbering activities

Each activity needs a unique identification code, in general, a number. In practice there are very elegant schemes. Most number activities in ascending order, that is, each successive activity has a larger number in such a way that the flow of activities is towards the completion of the project. It is customary to leave gaps between figures (1, 5, 10, 15...). Gaps are desirable for you to add new or missing activities later. Since it is almost impossible to draw a perfect project network, in general, network numbering is not done until the network is finished. In practice you will find computer programs that will accept numerical, alphabetical or combination designations of activities. Combination designations are often used to identify costs, work, skills, departments, and locations. As a general rule, activity numbering systems should be upstream and as simple as possible. They are thus intended for project participants to advance their work through the network and to locate specific activities.

Using computers to develop networks

The format is a two-dimensional representation of the project program, with activities in the columns and time along the horizontal axis. In this computer output the gray bars represent the durations of the activities. Lines that extend from the bars represent the slack time. For example, "software development" lasts 18 units of time (the shaded area of the bar) and 20 days of slack (which are represented by the extended line). The bar also indicates that the activity has an early start on January 3 and will end on The 20th of that month, but that it could be extended to February 9 because it has 20 days of extension. When dates are used on the time axis, Gantt charts provide a clear overview of the project program and can often be found on project office dashboards. Unfortunately, when projects have many dependency relationships, dependency lines soon become overwhelming and defeat the simplicity of Gantt's chart.

Project management software can be a great help in the hands of those who understand and are familiar with the tools and techniques discussed in this text. However, there is nothing more dangerous for someone to use the software with little or no knowledge of how the software produces information. Errors in information entry are very common and require someone who has a kn skills with

concepts, tools, and information system to recognize that errors exist and that false actions are being avoided.

Calendar dates

Ultimately, you'll want to assign calendar dates to your project activities. If a computer program is not used, the dates are assigned manually. Extend a calendar of business days (exclude non-working days) and number them. Then relate the calendar business days to those in your project network. Most computer programs will automatically assign dates once you have identified start dates, time units, non- business days, and other information.

Beginnings and multiple projects

Some computer programs require a common startup and termination event in the form of a node (generally a circle or rectangle) for a project network. Even if this is not a requirement, it is a good idea because it avoids "confusing" routes. They give the impression that the project does not have a clear principle or purpose. If your project has more than one activity that can start when the first one needs to start, each route is confusing. The same is true if the project network ends with more than one activity; these un connected routes are also called "Hanging Paths". They can be avoided by linking activities to a common project start or end node.

When multiple projects relate to each other in an enterprise, using a common start or end node helps identify the total planning period for all projects. Using false or fake waiting activities from a common start node allows different start dates to exist for each project.

Expanded network techniques to get closer to reality

The method that shows relationships between activities in the last section is called the start-to-end relationship because it assumes that all previously connected preceding activities must be completed before the next activity can begin. In an effort to get closer to the realities of projects, some useful extensions have been added. The use of escalations was the first obvious extension that practitioners considered very useful.

Scaling

The assumption that all previous activities must immediately be completed at 100% is very limiting in some situations in practice. Restriction occurs most often when one activity is translaperated over the start of the other and has a long duration. Under the start-to-end ratio standard, when an activity has long duration and will delay the start of activity that follows closely, the activity can be broken down into segments and it is possible to draw the network using the scaling approach, so that the activity that follows begins early and does not delay the work. This segmentation of the larger activity gives the appearance of advancing on a ladder

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BASIC RULES TO FOLLOW IN THE DEVELOPMENT OF PROJECT NETWORKS

Course:  Project Management (ADMG 374 )

15 Documents
Students shared 15 documents in this course

University: Central Washington University

Was this document helpful?
BASIC RULES TO FOLLOW IN THE DEVELOPMENT OF PROJECT NETWORKS
The following eight rules apply broadly when a project network is being developed.
1. Networks usually flow from left to right.
2. An activity cannot begin until all connected preceding activities have been
completed.
3. Arrows in networks point to precedence and flow. They can also cross each
other.
4. Each activity must have a unique identification number.
5. The activity identification number must be greater than that of the activity
preceding it.
6. Closed circuits are not allowed (in other words, no recycling should be done
through a set of activities).
7. Conditional assertions are not allowed (i.e. such assertions should not
appear. If successful, do something, other than do nothing).)
8. Experience suggests that when there are many beginnings, a common
startup node can be used to clearly indicate where the project will start on
the network. It is also possible to use a single end of the project to indicate
an end clearly.
Node Activity Basics (AEN)
The high availability of personal computers and graphics programs has served as
an impetus to use the node activity method (AEN, sometimes referred to as the
precedence diagram method). An activity is represented by a node (box). This one
can take many forms, but in recent years it has been depicted more than anything
as a rectangle (box). Dependencies between activities are represented by arrows
between rectangles (boxes) in the AEN network.
Arrows indicate how activities relate and the sequence in which things should be
accomplished. The length and slope of the arrow are arbitrary and are set for
convenience to draw the net. The letters on the boxes are used to identify activities
while learning the basics of building and analyzing networks. In practice, activities
have identification numbers and descriptions. There are three basic relationships
that need to be established for activities that are included in a project network.
Relationships can be determined after answering the following three questions for
each of the activities:
1. What activities should be completed immediately prior to this activity? These
are called ancestor activities.
2. What activities should you follow immediately to this activity? These are
called successor activities.

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