Chapter Six
Activity networks
It is a network which shows the different activities making up a project, their estimated duration, and their interdependencies.
These help us to:
Assess the feasibility of the planned project completion date
Defining activities
Activity networks are based on some assumptions: A project is:
Composed of a number of activities
May start when at least one of its activities is ready to start
Defining activities -continued
An activity
Must have clearly defined start and end-points Must have resource requirements that can be forecast: these are assumed to be constant throughout the project
Identifying activities
There are 3 approaches to identify activities: Activity based approach
Product based approach Hybrid approach
Work-based: draw-up a Work Breakdown Structure (WBS) listing the work items needed
Product-based approach
list the deliverable and intermediate products of project – product breakdown structure (PBS)
Identify the order in which products have to be created
Start and finish times
Activity ‘write report software’ Earliest start (ES)
Earliest finish (EF) = ES + duration
Latest finish (LF) = latest task can be completed without affecting project end Latest start = LF - duration
Example
earliest start = day 5 latest finish = day 30 duration = 10 days
earliest finish = ? latest start = ?
Float = LF - ES - duration
notation
Activity label, activity description
Duration
Earliest
start
Earliest
finish
Latest
Forward pass
Forward Pass is carried out to calculate the earliest dates on which each activity may be started and completed.
Start at beginning (Day 0) and work forward following chains.
Earliest start (ES) date for the current activity = earliest finish date for the previous
When there is more than one previous activity, take the latest earliest finish
EF = day 7
Complete the table
Activity ES
duration EF
Backward pass
This method calculates the LATEST DATE at which each activity may be started and finished without delaying the end date of the project. Start from the last activity
We assume that Latest finish (LF) for last activity = earliest finish (EF) of that activity.
If there are more than one activities as last activity, we consider activity which has highest EF .
We work backwards .
Complete the table
Activity ES Dur EF LS
LF
A
FLOAT
• Float is a measure of how much the start or
completion of an activity may be delayed without affecting the end date of the project.
• Any activity with a float of ZERO is critical , because
any delay in carrying out the activity will delay the completion date of the project.
Float = Latest finish - Earliest start - Duration
OR
Complete the table
Act-ivity
ES Dur EF LS
LF
Float
Critical path
Path : in activity network graph is any set of consecutive nodes and edges in this graph from the starting node to the last node.
Critical Path consists of a set of dependent tasks that need to be performed in a sequence and which together take the longest time to complete.
It defines the duration of project.
Note: the path through network with zero floats
Critical path: any delay in an activity on this path will delay whole project
