Task dependencies in developing project network diagram

In assessing the impact of constraints on determining task dependencies for development of a project network diagram, it is pertinent to understand the terms as used in relation to project life cycle. Project Diagram: ‘A pictorial representation of the sequence in which project work can be done’ (Wysocki, 2012). Verillon Advisory noted that the visual presentation (graphically) of all tasks in the project, or one of the workstreams of a project, and their relation to each other creates the project network diagram(Verillon Advisory, 2011) Dependency: ‘A relationship between pairs of tasks’ (Wysocki, 2012) It is a logical relationship which determines the sequence project task need to be performed.

Four task dependencies include: Finish-to-Start(FS): Task A must be complete before task B can start.(Wysocki, 2012) An example in a road construction project, route survey must be completed before earthworks can start. Start-to-Start(SS): The dependency relationship supposes that a successor task may start after the predecessor commences. The relationship doesn’t necessarily mean they must start together, they ‘simply require that the successor task can only begin after the predecessor task has commenced.

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’(Microsoft, 2010) Using our road project again, earthworks must begin before construction of storm drains. Start-to-Finish(SF):

This denotes a complex relationship The dependency is inverse as the successor cannot be completed before the predecessor has begun. Like in our road project, earthworks cannot finish before procurement of stonebase. Finish-to-Finish(FF): This dependency relationship intones that a pre-ceeding task must end before the proceeding task can end. In our example, road markings can only be finished when asphalting has ended.

Constraints:
Constraints determine the type of relationship between tasks in a project. It is the basis for sequencing. Each type of constraint can generate any of the dependencies listed above. Four types of constraints which affect the dependent relations between project tasks include Technical Constraints;
Management Constraints; Interproject Constraints; and Date Constraints. Technical constraints are a result of the requirements for fulfilling a given task which requires the result of a prior task.

‘There is no flexibility when the technical constraint links the tasks- they must be completed in a certain sequence. The tasks linked by the technical constraint usually create a critical path of the project.’(Verillon Advisory 2011) Management constraints arise when the leadership of the organization undertaking the project or client decides to drag a process in anticipation of changes, pending decisions, or events in relation to the task. Constraints of this manner are reversible Interproject constraints arise when the results of the tasks from one project are required in order to complete the tasks from another project. This usually occurs in complex projects where various players are involved in meeting a WBS which takes the dimension of projects of their own. Date constraints condition the task schedules by narrowing when they start and finish. 3 variants of this constraint includes: No earlier than(stipulates earliest date for task completion); No later than(stipulates a must date by which task have to be delivered); and On this date(stipulates exact date of task delivery.

Effect of the Constraints on task Sequencing
The technical and interproject constraints influence the order in which the tasks are to occur (Verillon 2011) They basically stipulates precedence and order of sequencing in task scheduling. The date constraints determines the duration for each component of the tasks and aides the project manager to arrange a project schedule. The management constraints brings in to play the necessity for contingency timeline in any task. Falling back on them will wedge the task from overshooting schedule.

References:
Luecke, R. (2004) “Managing Project Large and Small. The Fundamental Skills for Delivering on Budget and on Time”; Harvard Business Essentials; Harvard Business School Press; Massachusetts

Project Insight: (1997) :Understanding Task Dependencies in Project Management
Microsoft Projects: (2010): Back to Basics: Understanding task dependencies Verillon Advisory Services (2011): Task dependencies and their role in in developing a project network diagram

Wysocki, R. (2012) “The Effective Project Management: Traditional, Agile, Extreme” Sixth Edition. Indianapolis: Wiley Publishing