A task network displays the “how” of a project horizontally, from left to right. It shows dependency relationships among tasks. The task network concentrates on the critical path for resource deployment. For small projects of 25 tasks or fewer, it is possible to develop your network manually. Many people who are familiar with an automated project management system use the system-even for small projects.
The Precedence Diagramming Method
The Precedence Diagramming Method (PDM), a task-on-node system to represent elapsed time by a node. In recent years, the PDM chart has become widely used because they are easier to create and apply. A task network is a horizontal display of the flow of project work. The discipline required to create a task network identifies the components of the project that must go on in series and those that can be done in parallel with other tasks.
With it, you can identify:
• The start and finish of a project, each represented by a node
• Every task necessary to accomplish all project work, each represented by a node
• Tasks that must be accomplished in a specific series, displayed on paths
• Tasks that can be accomplished simultaneously or in parallel with others
• Dependency relationships between all predecessors and successors
• The critical path
If you use project management software, you can easily create and print a variety of task networks, one for each of your audiences if necessary. Because each audience may have different information needs, a different format or file can be created for each report. Higher levels of management only require summary reports
The information within each node can be chosen from many choices.
• Task name, WBS number
• Early start (Es-earliest possible start date)
• Early finish (EF-earliest possible 6nish date)
• Late start (LS-the latest the task can start without delaying any successor)
• Late finish (LF-the latest the task can finish without delaying successor)
• Responsible person, Slack time
Predecessors and Successors
A task network demonstrates how each task or activity relates to others in the project and shows the dependency relationships between and among all tasks. The Start node normally has only one successor task such as Objectives of the project. A successor is a task that must follow a given task. A predecessor is a task that must take place before a given task. As you begin to add nodes, you have part of a path. Additional nodes may be parallel to other nodes and that means that there can be multiple paths and two or more tasks can proceed simultaneously provided resources are available.
Dependency relationships among tasks are generally “finish-to-start” dependencies that require a predecessor to be completed before its successor(s) begins. Sometimes a successor can or must begin when part of its successor is accomplished. Task schedules can overlap and create partial dependencies. A partial dependence is a relationship that requires or allows a certain portion of a predecessor to be complete before its successor begins. For example, analysis of market research data can begin before all of the surveys have been returned.
Gaps or lags can also occur between the finish of one task and the beginning of its successor(s). A gap or lag exists when there is a need to wait for some period of time after the completion of one task before work can begin on its successor(s). This often occurs while waiting for approval after a proposal has been submitted or while waiting for paint to dry.
Two other types of dependencies are sometimes used. A “start-to-start” dependency is a relationship that requires or allows a task to start at the same time as another task. For example, it is possible to prepare for the data analysis on the marketing research project at the same time as the surveys are sent out. A “finish-to-finish” dependency is a relationship that requires or allows a task to finish simultaneously with another task. For example, in the same marketing research project, the analysis completion could be scheduled for the same day as the cutoff date for survey returns.
Analyzing Project Flow
There are at least three techniques you can use to analyze dependency relationships and to identify the predecessors and successors for all project tasks:
1. Project management software will calculate and analyze all relationships.
2. Sticky notes arranged on a wall or board can show all dependency relationships.
3. Dependency analysis worksheet can be written for later entry into your project management software.
Whichever method you choose, consult appropriate members of the project team, particularly those working on the less familiar, or breakthrough, aspects of the project. For those who are not present at the meeting, gather information or update them by email, fax, telephone, or one-on-one meetings. For larger projects, it may require several iterations to combine a number of sub-projects and create a network that accurately conveys the flow of project work. When complete, this network will be one of the most important tools in updating and managing the project. The analysis is complete when a task network is created and validated.
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