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NETWORK DIAGRAMMINGTECHINIQUES AND THEIRIMPORTANCE
PRESENTERS:
Sadia Nosheen 2k9-che-40
Zia ullah 2k9-che-64
Fakhar Abbas 2k9-che-122
Waqas Ali 2k9-che-149
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CONTENTS
Definition
Types of network diagramss
PERT & CPM
Differences between PERT & CPM
Terminologies Creating a PERT/CPM diagram
Importance of network diagramming techinique
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Project Time Management
Project time management involves the processesrequired to ensure timely completion of a project.Processes include:
Activity definition Activity sequencing
Activity duration estimating
Schedule development Schedule control
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Schedule development
Schedule converts action plan intooperating time table
Basis for monitoring and controlling project
Scheduling more important in projects thanin production, because unique nature
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Project Network Diagrams
Project network diagrams are the preferredtechnique for showing activity sequencing
A project network diagram is a schematic displayof the logical relationships among, or sequencing
of, project activities Graphical portrayal of activities and event
Shows dependency relationships betweentasks/activities in a project
Clearly shows tasks that must precede(precedence) or follow (succeeding) other tasks ina logical manner
Clear representation of plan a powerful tool forplanning and controlling project
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Network Diagrams CPM
PERT
Bar Charts Milestone Chart
Gantt Chart
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Network Diagrams Developed in the 1950s
A graphical representation of the tasks necessary
to
complete a project
Clearly visualizes the flow of tasks &relationships
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Terminology Activity - A specific task or set of tasks that are
required by the project, use up resources, andtake time to complete
Event - The result of completing one or more
activities. An identifiable end state occurring at aparticular time. Events use no resources.
Network - The combination of all activities andevents define the project and the activityprecedence relationships
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Path - The series of connected activities (orintermediate events) between any two events in anetwork
Critical - Activities, events, or paths which, ifdelayed, will delay the completion of the project.
A projects critical path is understood to meanthat sequence of critical activities that connect theprojects start event to its finish event
Dummy Activity
Indicates only precedence relationships
Does not require any time of effort
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A dummy activity may be needed:
to prevent 2 or more activities sharingthe same starting and ending events.
to maintain network logic i.e. toensure that the network abides by the
precedence table.
OK, tellme theworst!!
Sometimes we have to use
Dummy activities.
We use a dashed arrow
to record these.
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Arrows An arrow leads from tail to headdirectionally
Nodes A node is represented by a circle
ACTIVITYPRECEEDING SUCCESSOR
EVENT
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Network Diagrams Two classic formats
AOA: Activity on Arrow
AON: Activity on Node
Each activity labeled with
Identifier (usually a letter/code)
Duration (in standard unit like days)
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Formats
Activity-on-arrow (AOA)
Arrows represent activities and nodes are eventsfor points in time, It uses an arrow to depict anactivity.
The length of arrow shows relative time
to complete tasks
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Activity-on-node (AON)
Nodes represent activities, and arrows showprecedence
relationships, It uses a node to depict anactivity.
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Project Network Rules
Networks typically flow from left toright.
An activity can not begin until all of itspreceding activities are complete.
Arrows indicate precedence and cancross over each other.
Are there any rules tofollow when drawingnetwork diagrams?
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Identify each activity with a uniqueidentifier, this identifier must increment(1.2.3, A,B,C etc) as the network proceeds.
Looping is not allowed.
Conditional statements are not allowed.
Use the start and stop nodes
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Time-Related Task
Properties
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Situations in network
diagram
A
B
C
A must finish before either Bor C can start
A
B
C both A and B must finish
before C can start
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D
C
B
A
both A and C must
finish before either ofB or D can start
A
C
B
D
DummyA must finish beforeB can start
both A and C mustfinish before D canstart
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Example
Develop the network for a project with followingactivities and immediate predecessors:
Activity Immediatepredecessors
A -
B -
C B
D A, C
E C
F C
G D,E,F
Try to do for the first five (A,B,C,D,E) activities
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Network of first five activities
1 3 4
2
5
We need tointroduce a
dummy activity
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Network Diagrams
NETWORK TECHNIQUESNETWORK TECHNIQUES
PERT
-Program Evaluation andReview Technique
- developed by the USNavy with BoozHamilton Lockheed
- on the PolarisMissile/Submarineprogram 1958
CPM
Critical Path Method
Developed by ElDupont for ChemicalPlant ShutdownProject- about
same time as PERT
Both use same calculations, almost similarMain difference is probabilistic and deterministic in time
estimationGantt Chart also used in scheduling
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Critical Path Method (CPM)
The Critical Path Method (CPM) is one of severalrelated techniques for doing project planning.CPM is for projects that are made up of a number
of individual "activities." If some of the activitiesrequire other activities to finish before they canstart, then the project becomes a complex web ofactivities.
It is used for one time estimations.
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CPM can help to figure out :
1. how long the complex project will take tocomplete
2. which activities are "critical," meaning that theyhave to be done on time or else the whole project
will take longer
WOW
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If you put in information about the cost ofeach activity, and how much it costs to
speed up each activity, CPM can help tofigure out:
1. whether you should try to speed up the project,
and, if so, 2. what is the least costly way to speed up the
project.
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Example
Right, nowwell solve
an exampleof CPM
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Doingwell!!!
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Keep going!!
Find the total path and the critical path
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Critical path
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A Critical Path is a specific set of sequential tasks upon
which the project completion date depends
Tasks on the critical path cannot be delayed without
delaying the project completion day If a task on the critical path is delayed by 1 day, then
the project completion date is delayed (at least) by 1
day
All projects have at least one Critical PathCritical Paths are the paths with duration = total project
duration
CPM Ad t d
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CPM: Advantages and
Disadvantages
Advantages Show precedence well
Reveal interdependencies not shown in other
techniques Ability to calculate critical path
Ability to perform what if exercises
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Disadvantages
Default model assumes resources are unlimited You need to incorporate this yourself (Resource
Dependencies) when determining the real CriticalPath
Difficult to follow on large projects
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Purpose
To simplify the planning and scheduling of largeand complex projects.
To incorporate uncertainty in the sense that it waspossible to schedule a project not knowingprecisely the details and duration's of all theactivities.
Event-oriented technique rather than start- andcompletion-oriented.
Used more in R&D-type projects where Cost is not
a major factor but Time is.
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Terminologies
PERT event: is a point that marks the start or completionof one (or more) tasks. It consumes no time, and uses noresources. It marks the completion of one (or more) tasks.It is not reached until all of the activities leading to that
event have been completed. Predecessor event: an event (or events) that immediately
precedes some other event without any other eventsintervening. It may be the consequence of more than one
activity. Successor event: an event (or events) that immediately
follows some other event without any other eventsintervening. It may be the consequence of more than one
activity.
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PERT activity: is the actual performance of a task. Itconsumes time, it requires resources (such as labor,materials, space, machinery), and it can be understood as
representing the time, effort, and resources required tomove from one event to another. A PERT activity cannotbe completed until the event preceding it has occurred.
Optimistic time (O): the minimum possible time requiredto accomplish a task, assuming everything proceeds betterthan is normally expected
Pessimistic time (P): the maximum possible time requiredto accomplish a task, assuming everything goes wrong(but excluding major catastrophes).
Most likely time (M): the best estimate of the timerequired to accomplish a task, assuming everythingproceeds as normal.
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Expected time (TE): the best estimate of the time
required to accomplish a task, assumingeverything proceeds as normal (the implicationbeing that the expected time is the average timethe task would require if the task were repeated
on a number of occasions over an extended periodof time).
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Creating a PERT DiagramSTEPS 1:
Determine the tasks that the project requires andthe order in which they must be completed
Determine the optimistic, most likely, andpessimistic time of each task
Compute for the Expected time using the formula
Te=(O+4M+P)/6
Determine whether to use AOA or AON diagrams
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Activity Predecessor Optimistic(a)
Normal(m)
Pessimistic(b)
Te(a+4m+b)/6
A --- 2 4 6 4.00B --- 3 5 9 5.33
C A 4 5 7 5.17
D A 4 6 10 6.33
E B, C 4 5 7 5.17
F D 3 4 8 4.50
G E 3 5 8 5.17f
Rightnowwell solveanexample
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Start
F
C
GE
D
B
A
Finish
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STEPS 2: Determine the ES & EF of each activity by:
Start at the beginning moving towards the end
ES & EF for the start activity is always 0 since they aremilestones
Use the EF of the predecessor activity as the ES of thecurrent activity
EF of an activity is computed by adding its ES with itsduration
For activities with 2 or more predecessor activities, usethe predecessor with the higher EF as the ES of thecurrent activity
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Creating a PERT Diagram
STEPS 3:
Determine the LS & LF of each activity by:
Start at the end and work towards the beginning
Use the LS of the successor activity as the LF of thecurrent activity
LS of an activity is computed by subtracting its LF withits duration
For activities with 2 or more successor activities, usethe successor with the lower LS as the LF of the currentactivity
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Creating a PERT Diagram
STEPS 4:
Compute for the critical path by adding theduration's of various paths for all activities
Determine if any activities have slack by
subtracting the activitys LF & EF
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PERT & CPM Similarities
Both follow the same steps and use network
diagrams Both are used to plan the scheduling of individual
activities that make up a project
They can be used to determine the earliest/lateststart and finish times for each activity
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PERT & CPM Differences
PERT is probabilistic whereas CPM is deterministic
In CPM, estimates of activity duration are basedon historical data
In PERT, estimates are uncertain and we talk of
ranges of duration and the probability that anactivity duration will fall into that range
CPM concentrates on Time/Cost trade off.
ADVANTAGES:
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ADVANTAGES:PERT chart explicitly defines and makes visible
dependencies (precedence relationships) between the
work breakdown structure (commonlyWBS) elementsPERT facilitates identification of the critical path and
makes this visible
PERT facilitates identification of early start, late start,
and slack for each activityPERT provides for potentially reduced project duration
due to better understanding of dependencies leading
to improved overlapping of activities and tasks where
feasible.
The large amount of project data can be organized &
presented in diagram for use in decision making.
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DISADVANTAGES
There can be potentially hundreds or thousands of activities
and individual dependency relationshipsPERT is not easily scalable for smaller projectsThe network charts tend to be large and unwieldy requiringseveral pages to print and requiring special size paper
The lack of a timeframe on most PERT/CPM charts makes itharder to show status although colours can help (e.g.,specific colour for completed nodes)When the PERT/CPM charts become unwieldy, they are nolonger used to manage the project.
Importance of a Network Diagram
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Importance of a Network Diagram
Visual Imagery:
It can be quite difficult for non-technical people tounderstand how a particular piece of softwareworks, and why its proper operation is so criticalto the success of the business. The network
diagram includes pictures that show each step inthe software process, from inputting the data todistributing the resulting reports.
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Faster Education:
Creating a detailed network diagram that shows
how a particular piece of software interfaces withcompany hardware and other pieces of softwareallows both new hires and existing employers togain a better understanding of the work they need
to do and how their particular jobs affect theentire organization. The ability to see each step inthe software development and softwaremanagement process in visual form is often
helpful for workers in the IT field and formembers of the management team.
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Better Record Keeping:
Documentation is a critical, but often overlooked,
part of any IT organization. Without the properdocumentation in place it can be difficult to trackdown problems in complex systems. By taking thetime to create a detailed network diagram for
each piece of software used in the company, theIT staff makes it easier for their colleagues to findand resolve problems, even if they have no directexperience with that type of software.
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Better Project Planning:
A detailed network diagram allows project managers andother members of the project team to plan their projects
more effectively. When everyone on the project team cansee exactly how the software works, and what othersystems it interfaces with, it is much easier for those teammembers to move forward with beneficial changes. A
good network diagram also allows project teams to avoidcostly mistakes that could have an impact the operation ofthose software packages and the networks on which theyrun. In fact, the Project Management Institute cites theimportance of network diagrams in their trainingmaterials and other literature.
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REFERENCES
www.smartdraw.com/specials/network.asp
www.edrawsoft.com/Network-Diagram-Tutorials.php
www.opnet.com/solutions/network_management/netmapper.htm
www.slideshare.com
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Thank You
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