Critical path analysis Flashcards
What is a precedence table?
A table which shows the activities that each activity is dependent on
What is an event?
The completion of an activity
What is an activity on arc network?
A way of representing each activity’s dependencies in network form
Describe an activity on arc network
The activities are represented by edges, and the events are represented by vertices. Each edge has an arrow defining its direction. It is convention to use straight lines for edges
What is a source vertex?
A vertex with an indegree of 0
What is a sink vertex?
A vertex with an outdegree of 0
What is a dummy activity?
An activity which has no weight, but is used when it is otherwise impossible to show an activity being dependent on several events, or to avoid two activities sharing an edge
What is the early event time of an event?
The earliest possible time that it can occur
How can the early event time of an event be calculated?
Starting from the source vertex and working forwards, it is the longest possible path into the event
What is the late event time of an event?
The latest time that it can occur without delaying the overall time of the project
How can the late event time of an event be calculated?
Starting from the sink vertex and working backwards, it the longest possible path into the event subtracted from the sink vertex’s early event time
What is the float of an activity?
The amount of time that its start may be delayed without affecting the duration of the project
How can the float of an activity be calculated?
Latest finish time - duration - earliest start time
What is a critical activity?
An activity with a float of 0
What is a critical path?
A path from the source vertex to the sink vertex which entirely follows critical activities
What can be said about the vertices on a critical path?
The early event times and the late event times are equal
Describe a Gantt chart
The number scale represents elapsed time. The critical activities are all shown on the same line at the top. All other activities are shown on their own line, with a solid box representing the earliest start time and the duration, while a dotted box extends to the latest finish time, showing its float
How can one work out which activities must be happening on a certain day from a Gantt chart?
It is all activities whose solid box must lie on the imaginary vertical line drawn on the appropriate time
How can one work out which activities may be happening on a certain day from a Gantt chart?
It is all activities whose solid box may lie on the imaginary vertical line drawn down the appropriate time after being moved around within its dotted box
What assumptions must be made when scheduling?
- Each activity is completed by a single worker in the time given as the duration of the activity
- Once an activity has started, it must be completed by the worker
- Once a worker has completed an activity, they become immediately available to start another activity
Which worker should always be used when scheduling?
The first available one
What should be done if there is a choice of tasks for a worker?
Assign the one with the lowest latest finish time
