D1, C8 - Critical Path Analysis Flashcards
What goes in the two columns of a precedence / dependence table
Column 1 - Activity (A, B, …)
Column 2 - Dependence (what the activity depends on)
What type of graph can you display a precedence / dependence table on
An activity network
What is the node at the start and the node at the end of an activity network called
Start - source node
End - sink node
What does it mean if an activity network is an ‘activity on arc’ network
The activities are on the arcs (between nodes) as opposed to ‘activity on node’ networks where the activities take place on the nodes
How do you number nodes on an activity network
Number them as they are added to the network (chronological order)
What does a dummy activity show
Precedence
Do dummy activities incur a cost or time
NO
When do you get dummy activities
When an activity (C) is dependent on just one other activity (A), but another activity (D) is dependent on the same activity as C (A) but also another activity (B)
How do you draw dummy activity lines
Dotted lines
What is the time it takes to complete an activity called
Its duration
What is an early event time
The earliest time an activity can start / finish
What is a late event time
The latest time an activity can start / finish
How do you show early and late times on an activity network
Replace nodes with two boxes, top box is the early event time, bottom box is the late event time
What numbers go in the early and late time box for the source node
0, 0
What numbers go in the early and late time box for the sink node
The SAME number
How do you find the early event time
Perform a forward pass/scan
Longest time to finish
How do you find the late event time
Perform a backward pass/scan
Shortest time to start
For a forward pass do you pick the highest or lowest option
Highest
For a backward pass do you pick the highest or lowest option
Lowest
What is a critical activity
An activity which will delay the finish time of the project if it is delayed
What is a critical path
A path which goes from the source node to the sink node only through critical activities
What is true of the early event time and late event times for a critical activity
They are equal
Early event time = late event time
Where do critical activities often (not always) happen between
Between critical events
Can you have multiple critical paths
YES
What is the float of an activity
The amount of time that the start of the activity may be delayed by, without delaying the finish time of a project
How do you calculate the total float for an activity
Total float = latest finish time - duration - earliest start time
What do Gantt (or Cascade) charts show
The activities on a network
What do solid rectangles represent on Gantt charts
Activities
What do dotted lines represent on Gantt charts
Delays to activities (floats)
Where do you put critical activities on a Gantt chart
On the top row
What do resource histograms display
The number of workers needed for an activity
How many activities can one worker be assigned to on a resource histogram at a time
1 activity at a time
When can workers stop their activity on a resource histogram
When they have finished it
How long after finishing an activity does it take for a worker to start a new activity on a resource histogram
Immediately available
What is levelling with resource histograms
The process of adjusting the start / finish of activities to take into account any constraints on resources
What goes in the x and y axis for a resource histogram
y = number of resources needed per activity (workers)
x = time needed per activity (days / hours / etc)
For scheduling diagrams how many workers are assumed to be required per activity
One worker assumed to be required per activity
For scheduling diagrams which worker do you use
The first available worker
For scheduling diagrams, if we can choose more than one activity to assign a worker to, which activity do you choose
Choose the activity with the lowest last time
What is the formula to calculate the lower bound for the number of workers needed to complete a project by its critical late time
Lower bound = (sum of all activity times) / (critical time of the project)
(take the smallest integer >= the answer)
