Generating Network Diagram

To optimize the work under the project it is possible to generate the network diagram of the project.

• Briefly about network diagram
• Calculation and displaying early dates
• Calculating and displaying time slacks
  

The network diagram is a sequence scheme of work completion. Works (or operations) are represented in form of blocks (more often in form of rectangles) connected together with arrows. The network diagram spreads from left to right. Arrows always represent the link type finish to start (about types of links read in details in the chapter Links between tasks of this lesson) i.e. the task cannot be started until the previous task has been finished. If the task has several preceding tasks, such task is called as 'confluence operation'. If the task has several following tasks, such task is called as 'breakdown operation'.

Note: In network diagram the operation may consist of one or several tasks. But as soon as in ConceptDraw Project the network diagram is not created but generated from Gantt Chart which consists of tasks, so in network diagram each operation corresponds to 1 task.

As Gantt Chart is one of the main working tool, we will use the term "task" as well as in regard to components of network diagram (1 task=1 operation).

Representing the project as a network diagram gives additional advantages: dependent tasks are presented more visually so it is possible to determine which tasks have time reserve and for how long they can be delayed if necessary. Looking at the diagram it becomes obvious which of the tasks are critically significant and are to be performed strictly in time as their delay would entail the delay of the entire project.

To take advantage of Network Diagram, generate it on basis of Gantt Chart. For this:

Apply command Network Diagram from menu View

Task: Generate Network Diagram

Calculating Early and Late dates.

To determine possible delay of task completion as well as to define tasks which can't be delayed, Early and Late Starts and Early and Late Finishes of tasks are calculated.

Early parameters are calculated from start (direct analysis) where the Early Start of the first task is its beginning. Early Finish of any task is equal to its Early Start plus its duration. Early Start of the next task is the Early Finish of the preceding task. If the task has several preceding tasks (confluence operation) then its Early Start will be the Early Finish of the most prolonged task.Early Start is denoted with abbreviation ES, Early Finish -EF.

Late parameters are calculated from end (back analysis) where the Late Finish of the last task is its early finish. Late Start of any task is equal to its Late Finish minus its duration. Late Finish of the next task is the Late Start of the preceding task. If the task has several following tasks (breakdown operation) then its Late Finish is the Late Start of the most prolonged task. Late start is denoted with abbreviation LS, Late Finish- LF.

On the network diagram such parameteres as slacks of Early and Late Starts and Early and Late Finishes are displayed.

ESL- Early Slack of Early Start or Early Finish. If having time slacks it is possible to shift the date of task completion (Early Start and Finish) to the latest term. It is also possible to shift finish more than start, increasing the task duration. But any slack should be within the limits of early and late parameters.

LSL - Late Slack of Late Start and Late Finish. Such slack is undesirable as entails the delay of the entire project or forcing of following tasks.

This way Early start, Early Finish and supposed time of project completion are calculated by early parameters. Late Start, Late Finish, Crytical Path and slacks are calculated by late parameters.

Task: Define Early and Late dates for tasks "Choose a place", "Make up entertainment list" и "Make up equipment list".

Calculating and displaying time slacks

There is an interval between early and late parameters. This interval is called a 'slack'. Slack is always a positive number. If the number is negative this lets us know about some mistakes in calculations so the calculation should be redone. In program slacks have an abbreviation SL.

Advantages of knowing these parameters: slack gives much flexibility in disposition of limited resouces used in several parallel operations. If necessary it is possible to start tasks which have slack later then it is planned, but within the limits of early and late parameters.

Task: Define slacks for tasks "Choose a place", "Make up entertainment list" и "Make up equipment list".