Project Network Diagrams - Project Management

How to create a project network diagram from a WBS ( Work Breakdown Schedule). Shows how to then calculate the Scheduling times and the critical path using the Critical Path Method (CPM).

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Closed Caption:

this video tutorial is to do with the
question of making a network diagram
from a work breakdown schedule in the
context of project management
so to describe first of all what a work
breakdown schedule is work breakdown
schedule is usually a table that this
all the different tasks that have to be
completed for an overall project to be
complete
it lists what the estimated duration is
of all those tasks and it lists what the
dependencies are those tasks
so let's look at this one here in front
of us I've got a number of different
activities all labeled between a page
I've got all of the different estimates
of how long each of those different
activities will take to complete and
I've got all of the different
dependencies of those tasks
now what these dependencies mean is that
if I list for instance in the case of
taxi here any immediate predecessors
that means that i have to have these
tasks and be complete before I can start
ask see anywhere where I don't have any
immediate predecessors that means that
that task and start as soon as the
project started so i can see for task a
task be a nasty
I don't need to have any other tasks and
please
as soon as I start the project I can
start those tasks
what this question question certainly is
asking is to prepare a project natural
diagram to calculate the change in x and
total slacker agency and to list the
critical path activities and the project
duration
so let's have a look at that i'm going
to switch over to look at that nice to
that will allow me to draw out my
project diagram easily and just for easy
to use to have taken a screen print out
my work breakdown schedule and I have
copied in here at the top of this
diagram
so the first thing that we have to do in
any network diagram a project management
is we put in a startled is just shows
that the project is strategy and then
after that we can start to put in any of
these different tasks that i can start
straight away as soon as the project
started
and by that i mean in this particular
work great on schedule I mean task egg
because it doesn't have any predecessor
task because it doesn't have any
predecessor task because it doesn't have
any predecessor
so each of those different task can
start immediately and contestant
simultaneously with one another
so I'm going to draw on the different
tasks on this little diagram for a B&E
now at the end of this project diagram
I'm going to have all of the different
tasks with the predecessors or
interdependencies shore with Errol's for
the moment just for the first draft of
when I'm laying out my project
network diagram so that it's nice and
tidy just for the moment i'm not going
to draw in any different Errol's i'm
just going to do a brief kind of layout
first of all and then underlined the
arrows but I'm happy with that
with the layout and that i'm happy that
it will look tidy looking at the next
task that I want to put in here
the one that I skipped over there that
does have dependencies is task see and i
can see that c is dependent on me and be
to be finished before it can start so
I'm going to put the task see somewhere
over here so I can draw arrows easily
from a and B interceded shorter
dependencies the nest next task that
will be interested in is tasky so E is
dependent on the task see
so again i'm going to put e past see
somewhere over here and i'll just move
that into position next task i'm
interested in this task f task is
dependent on task T so again i'm going
to insert the task F and move it down
beside task T next
task but i'm interested in is task g and
it is dependent on e and f so i'm going
to insert task g and move it over
slightly over here so I can easily draw
arrows between E and F to G and then
lastly a got task h task age and said
and I put that past task geez i can
easily draw an arrow in here and my
natural diagram is taking shape
now i need to put in all the different
arrows to show all these different
dependencies and really could have done
that when i was doing all of those
different tasks and honorable together
but just I offered to do it this way so
that i can make sure that I try to avoid
any I was crossing over one another
so let me change my arrow - and i was
tagged drawing out between start and a
starter and be start and D and then I
need an arrow between a and B leading in
to see and going down to ease
dependencies I need an hour far
c d e and f is dependent on dee dee has
to finish before f can start supper and
I'll between them and g is dependent on
e and f
so I need to finish eat and as before
she can start and then Paige is
dependent on g so i put an hour between
those two there and let me just select
on my arrows out like to the slight but
picker creation
so that's a nice tidy
network diagram
it clearly shows all the tasks and it
clearly shows all the interdependencies
as well
it shows a definite floor from the start
of the project which tasks come first
and then as it moves through all the
different dependencies it moves to a
final point which is in task age
at this stage I want to start looking at
the different scheduling times and total
lack of each activity and it involves a
particular method numerical method which
is quite involved before I wanted that
just to make it easier for me to quickly
access the difference
estimated duration of all the different
tasks i'm going to put in a little
subscript at the bottom of each of these
different tasks that shows the estimated
duration of each of them and looking at
my work breakdown share your table
a is a constant situation of four be as
an estimated duration of 3d has an
estimated duration and have one see as
mr. next generation of five
we also have the best dad
estimated duration of 5 f as an
estimated duration of 2g has an
estimated duration of 5 NH as an
estimated duration of six now we're
ready to go ahead and attempt this
numerical method after finding all the
different scheduling times and total
lack of each activity which will explain
later
at the moment from my work brings our
schedule all of this information here is
now contained in my chart so I don't
need this table anymore will give me
more room
I can move my diagram of the little bit
and we can go ahead now and reduce the
different scheduling times of each of
the different tasks so to allow me to do
this
what I'm going to do is I'm going to
draw on a cross hairs beside each of the
different tasks and as best as i can i'm
going to try and get the man beside the
different tasks i usually go for the top
right hand side of me to the task
and you usually try and keep it
consistent remaining a little more bit
more space there
I just move some of these parts down
here and i'll just give me a little bit
more room so I can clearly see that
crosshair here so all of my different
tasks
we've all got across here just to the
top right of them now about these
classes of 4 i'm going to put in a
different number in each of the
different quadrants of these past years
and then finally at once i've done that
i can calculate as a different number
for total snack which are put at the top
to show what each of these different
numbers mean I'm going to put a legit
over out here at the top right of my
diagraph and the first text for the
first quadrant
what that is is I'm going to put it
there is es standing for our early start
meaning what is the earliest possible
start I can start an activity
the next number which is in the top
right quadrant is EF standing for early
finish
plus the earliest possible time I can
finish an activity for the moment i'm
just going to leave it that those two
because I just need to calculate those
two numbers for the first pass going
from left to right across my network
diagram so let's apply that logic to
some of these different tasks if i look
at ask a it can start immediately as
soon as the project and start
so the early as possible time I can
start task a is at day 0 so that's the
number i'm going to put in here in this
quiet
the area is possible start because a the
estimated duration is for days if I can
start the task of x 0 the earliest
possible time I can finish that task is
on day four
so the number i'm going to put in here
for early finish is for applying that
logic that I'm just after doing there
with task a to task be a nasty
both of these tasks can also start
as soon as the project starts so each of
them can start a day 0 so the early
start up a VAR b & E is x 0 so up 40
each one of those quads and then for
task be because it can start at zero and
it takes three days then the area's
possible time
I could finish task B is on day three
so put three into that quadrant and for
task d the earliest possible time I
could start asked to use 20
so the area is possible time I can
finish nasty given that has got an
estimated duration of one is day one and
one goes into that quadrant
now those areas task all of those task
and that could start signal taneously as
soon as the products tax
they're quite easy to find out what the
area is tacky nearly finished our let's
move on to some of the more kind of
complicated tasks for instance task see
I want to fill in a number for this top
left quadrant the area distractor task
see
so again i'm going to ask the question
what is the earliest possible time
I can start task see now this is more
tricky than what we've done with task a
B&E before because he is dependent on
both a and B to be finished before tasks
you can start
I have to have a and B finished and
completed before i can-- tasks before I
can start at sea
so if i look at the different finishing
times our task and task be to have be
finishes our day three at the earliest
possible time that the task a can finish
this day for so for me to be able to
stretch task see I have to wait for both
B and a to be finished and there for a
I'm going to take that number from the
early finish of a and there's a number
that i'm going to be putting in a bit
early start to see the earliest possible
time I can stand see is when he is
finished a day for so i take the four
from that quadrant and a place to 4 here
given that
task see as an estimate situation of
five days and the earliest possible time
I can start ask c is update form then
the area's possible time
I can finish taxi is 4 plus 5 which is
day 9
let's look at ass get task is dependent
on task to eat to be finished before it
can start so be early as possible to
finish your task d is the day one
so therefore the earliest possible time
I could start as get is day one
given that f as duration of two at the
earliest possible time I can finish task
f is one plus two is true
let's look at a ski
taski dependency to finish therefore the
earliest possible time I can start e is
when she finishes on day nine so that's
the number that i'm going to put in
I'll be released required to be and
given that he takes five days
the earliest possible time and finished
a ski is 9 plus 5 which is day 14
let's move down to task g
now again G is a little bit more
complicated than ers because I've got
two different dependencies there she is
dependent on e and f to be finished
before it can start so i have a choice
here whether take the 14 or three
so it was similar to the choice that
made back with tasks see when I had to
choose the early finish times are a or b
as the early start time of see the logic
again halls I have to hold off and wait
for both of these tasks to finish before
I can start ask g
so what if F has an early finish the
three and he has an early finish of 14
I have to wait for e da 14 so on the way
over at this forward pass
I always take the highest number of the
earliest and quadrants of the preceding
tasks the early start
LG is 14 the area is possible to finish
time is 14 plus 5 which is 19 and then
I've got task age is the only one left
and again that's a lot more
straightforward I've just got one
dependency there
so the area is possible start time is
day 19 and the earliest possible to
finish time is 1900 625
having the mood first pass across my
project natural diagram looking at all
the early start and early finishes of
all the different tasks i've come up
with this early finish number which is
our task age now task ages the last task
all the other tasks are feeding into it
therefore whatever this earliest finish
time or number is for task age that is
the overall duration of the entire
project this entire project the way that
has scheduled at the moment
it takes 25 days to complete all the
different tasks to complete the entire
project
you know just take note of that down
here at the bottom right of my diagram
I've mentioned a few times that all of
these numbers that we've done for the
early start in early finish quadrants of
my crosshairs on all the different tasks
that is the first pass going from left
to right across my diagraph now we're at
the stage where we can do the second
pass which is backwards right to left
across the diagram and before I do that
I need to fill in what the different
quadrants at the bottom of my crosshair
stand for the bottom left-hand quadrant
of the crosshairs
it stands for a late start what's the
lasers possible time
I can start this task but still keep the
overall project on track to finish in 25
days and the bottom right-hand quadrant
of my crosshairs is lead finish again
what's the latest possible time I can
finish this task but still keep the
overall project duration our track
I will understand this late start and
finish concept as we work backwards
through the task
so first of all it's cool for the last
task which is task age
what's the latest possible time I could
finished his cage but still keep the
overall project duration at 25 days
well at this last tag task is very very
simple
I have to finish it by 25 days if I want
to finish up by 25 days
so always if I've got this kind of
scenario where about converging tasks
coming into one particular time
at the end of the project the numbers at
the top of the class here is always at
the same as the numbers of the part
so the latest possible time I can
finished his cage is that day 25 and
still keep the overall project duration
of our track to finish and a 25 and
because page takes six days 25-6 is
equal to 19
that means that's the lid as possible
time
oh I can afford to let her age stats and
still keep the overall project schedule
our track
let's look at ask g again I'm going to
fill in the late finish quadrant first
of all lost a little as possible time
I could finish task g and still keep the
overall project duration on track to
finish 25 days
well i have to allow task page to start
a day 19
so the latest possible time I could
finish tasks gee I still keep the whole
project schedule on track is that day 19
I have to get finished by that time to
allow page to finish so i'm going to
copy that text box from here I'm going
to take that my team from there and put
it there as the lead finish in task G
because G takes five days to complete
the latest possible time I could start
task T and still keep the overall
project schedule our track is a day 14
that's a 19-5 let's look
the late finish for tasky what's the
latest possible time
I could finish tasky and still keep the
overall project duration on schedule
again
I have to get be finished by day 14 to
allow g2 to start by day 14 and keep all
the tracks on schedule so i am going to
take the 14 from here and put it into
this quadrant here task e takes five
days so 14-5 is 99 is the latest
possible i can start a ski and still
keep the overall project duration
archangel
let's look at ass gif
what's the latest possible time I could
finished as gift and still keep the
overall project duration are changeable
well to allow g to stop by da 14
I have to get task if finish by day 14
it doesn't matter so much that e and f
could possibly finish on the same day as
long as they're both finished in time
for g2 star today 14
that's fine so I'm going to take the
late start of g and i'm going to use it
as a late finish of it because the
duration of methods to 14 minus two is
twelve when looking at ask see what's
the latest possible time
I can finish tasks see and still keep
the overall project duration archangel
well I have to get it finished by day
line to allow you to start a day 9 so
day 9 is a little tipsy and 9-5 is for
let's look at task d & D down here to
allow life to start at day 12
i am going to make sure that he is
finished by day 12 as well so you can
see a pattern emerging here as well
I keep on looking at the following task
from the task of animal
dealing with at the moment and I pick
out the late start of that task 12 of F
in this case and I use that as the late
finish of the test i'm dealing with
so 12 let's start 40 is 12-1 is 11
now looking at ask be task B has to get
finished by day for to allow see to
start to date for so i'm going to take
the four from there and I'm going to
bring it back here for their 4 minus 3
is 1 so the late start
barbie is one and then lastly looking at
ask a
what's the latest possible time I can
finish tasks cape and still keep the
overall project schedule on track
well the leaves start of c is for i'm
going to take the 44 there and I'm going
to use it as a late finish of a and 4 -
40 and i love that into the lead start
position and that finishes the second
pass going from right to left across my
nipple time and now the final piece of
what happens to this legend over here is
a number that i'm going to put right
over the top of each class here in the
legend i'm going to put in the
abbreviation TS standing for total slack
or total slippage for the moment i'm not
going to explain what total slippage is
it will become clear when we go on to
the critical path method but it's enough
to see how to calculate the total
slippage is I just take the late finish
and subtract from us
the early finish number of each of the
different activities
so let me write that formula down if i
apply that formula to each of the
different activities
these are the numbers that i get for
activity age 25 - 25
equals 0 for active GG 19-19 equals 0
for activity ii 14-14 equals 0 for a GF
14 minus 3 equals eleven for activity d
12 minus 1 is equal to 11 for activity c
9 minus 9 equals 0 for activity a 4
minus 4 equals 0
and lastly for a two gb 4 minus 3 equals
1
so those are all the total slacks or
total slippages for the different
activities in this project natural
diagram at this stage no matter what
project Network diagram that we're
looking at there will always be at least
one path going from the start to the
finishing task that has a trail of zeros
on it now I see at least one because you
can't have more than one path but in
this project Network diagram
I just had the one going from the
stretch IC tag a taxi
taski task g and ask age all have zeros
for their total slippage this path in
any project Network diagram is known as
the critical path and i'm just going to
take an order of the critical path is
here
what the critical path means is that
these tasks have to be finished on time
on time
as regards their estimated duration for
the overall project to remain an
archangel
if there is any slippage or if there is
an e in the completion of these tasks
the overall project duration of 25 days
will slip having zero Slimbridge means
that there is no leeway on the other
hand these tasks then out of the
critical path B D and F they have a
certain amount of slippage
they have a certain amount of leeway so
for instance would task f
I have 11 days language which is quite
generous
meaning that as a project manager I
don't have to be overly worried about
the overall project schedule if task
starts to slip artists acetate Oh a
little bit longer and then it's expected
two days
it's the same or task T and task B of
the task be only has one day slippage
if task B goes from three days four days
it's not anything to panic about but if
it goes any more of the back then all of
a sudden it will have an effect on the
overall project duration so going
through the steps that we've seen in
this video tutorial we have created a
project natural diagram we have
calculated the change in x and the total
slack for each activity we've calculated
the overall project duration and we've
deduced it from all of that
what the critical path of this
particular project is this is all really
useful information for project managers
and this should be kept on hand for
measuring the project's progress
the overall label that I put on this
whole procedure is known as work
breakdown shared which project natural
diagram and the critical path method