task dependencies

Project Scope Definition(The Scope Triangle)

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Project Scope Definition(The Scope Triangle)

Every project, no matter how small, has tasks and activities based upon the requirements. Therefore, there is need to breakdown these activities into tasks until further breakdown is impossible or unnecessary for feasibility in managing the objects. This breakdown will help greatly in estimating the cost and duration of the entire project. Reference to PMBOK Guide (2008, p.103), the Project Scope Management, which is part of the Project Management Process Group, is characterized by:

  1. Collecting Requirement (Requirement Gathering)
  2. Project Scope Definition
  3. Project WBS Creation
  4. Verifying the Scope
  5. Controlling the Scope.

It is apparent that having gathered the project requirements, the scope of work to be performed in the project is defined thereupon. It is against this background the activities are identified to more manageable components, such as the landscaping, electrical, plumbing, furniture, painting and even roof work, for instance, in the renovation of the partially furnished building example, and resultant WBS (Work Breakdown Structure) that may include tasks and sub-tasks, as the case may be.


Why do we need WBS?

It is known that the Scope Management Knowledge Area overlaps the project initiation (scoping) and planning process groups (Wysocki, R., 2009, p.32). The requirement collection and documentation are precursors to determine the best-fit Project Management Life Cycle approach to be used, and subsequently developing the Work Breakdown Structure for effectively costing and scheduling (duration and resources). Hence the WBS is required in determining the various work packages inherent in the project. Heerkens, G.R. (2002, p.115) clearly indicates the objective of the WBS as identifying relatively small, specific pieces of work; and this will assist in creating a complete project plan.  In other words, WBS is a hierarchical structure, in details, of the project deliverables, which are any unique and verifiable product, result, or capabilities to perform a service that must be produced to complete a process, phase, or project (PMBOK, 2008, p. 424). This fragmentation of the tasks to the lowest possible level of task are very useful in task duration estimation, resource scheduling, and cost estimation – hence the need for the WBS.


Task/Activity Dependencies

Task dependencies as elaborated by Wysocki R.K. (2009, p. 161) are pair of activities that are related together and are represented by the activity flow diagram known as Project Network Diagram or Logic Diagram.

There are four types of dependencies, which are Finish-To-Start, Finish-To-Finish, Start-To-Finish, and Start-To Start as illustrated hereunder:

task dependencies
Task Dependencies Example

There are basically two proponent factors that may be helpful in determining or deciding task dependencies:

  1. The possibility of simultaneity of task (paralleling or fast tracking)
  2. The Start/Finish relationship between tasks; that is to say, which task precedes or succeeds the other in the activity network, which are usually represented using Precedence Diagramming Method (PDM), also known as Activities on Node (AON).


The above factors are evidently clear in the four types of dependencies:

  1. Finish-to-Start (FS): Task A is, completed before task B begins.
  2. Start-to-Start (SS): Both tasks A and B  begin simultaneously
  3. Start-to-Finish (SF): When activity A begins, B may finish.
  4. Finish-to-Finish (FF): Both activities (A & B) may be completed collectively.


Using the scenario of renovation of the semi-furnished house, painting work cannot start when the plumbing work are not completed in every instance (for example each rest room); this is a Finish-To-Start dependency type.

However, the roofing and landscaping activities may begin simultaneously without distortion, which depends on the resource availability, though. This is a Start-To-Start dependency type.

The electrical work may be done in parallel with the plumbing work especially if conduit electrification is employed. This will be useful and necessary if Fast Tracking (paralleling of activities, which were originally planned to be sequential) is required at some instance of the electrification.


It is now observable that the duration of the project is affected by the relationship between activities. If all activities can be performed simultaneously for any given project, say, which is a Start-To-Start dependency type, then obviously, the project execution duration of such project will be far shorter than project with lots of predecessors and successors; unfortunately, there are no such projects with all tasks parallel. The foremost significance of activity dependencies is pronounced in the Project Network Diagram in that it benefits the project managers with extra information (Wysocki, R.K., 2006, p. 522) such as:

  1. The best possible earliest time to complete all activities/tasks in the project.
  2. The earliest expected date of completion.

It is pertinent to note that dependent tasks graphically represented, of the project schedule, depends solely on the tasks, their inter-relationships, and their durations (Wysocki R.K., 2009, p. 162). As such, the impact of the task dependency of the project duration cannot be overemphasized as it is evident.

In most projects, several people are working on different activities at the same time and many activities are dependent upon one another, especially relatively very large projects, so it’s virtually impossible to manage a project from just a list of activities (Heerkens, G.R., 2002, p.124). This is where the need for task dependencies identification comes to play. 


It is also important to note that controlling the scope is more feasible after the WBS are identified due largely to the extent of details of the non-decomposable level of tasks, which are easy to estimate in terms of project scheduling, costing, resource management, procurement management, quality assurances, scope change management, risk, and communication management.



It is very important to breakdown the sequence of activities in a project, and identify the interrelation with one another.   Despite the scope of the project, even if it is a single work package, there is bound to be series of work to be done, and it is wise to ensure that proper disintegration of the activities is made to ensure quality and efficient production of final deliverables. The renovation of a living room, which includes painting and furniture only, still, requires a WBS. The WBS is dependent on the requirements gathered / collected. Thus, changing/ replacement of existing furniture, transportation, and installation, are a few tasks inherent therein. Similarly, for the painting, colour, type of paint, and preparation of the areas in the living room are potential tasks that are worthwhile. The walls may need scrapping as stated in the project requirement (included in the scope), which is part of painting activity, and should all be included in the WBS dictionary.

Now, there are certain constraints that impact the timing and scheduling of resources during project execution. These constraints are limitations that impede the project activities in its progress. MANDRAS (2008, p.18) in Project Time Management, categorized these constraints into mandatory (for instance foundation of a building, and technical requirements), discretionary (based on logical and experiential reasoning), and external dependencies, such as standards, government policies, and/or vendors’ deliverables. Nonetheless, by clearly ascertaining the WBS, and task dependencies based on the constraints and requirements, the easier risk analysis is possible, cost estimation is easier; resource levelling is more feasible; identification of missing functions and features for higher product quality becomes apparent.

Conclusively, the WBS should not be ignored for any project regardless of the scope or size.



PMBOK Guide (2008). A Guide to the Project Management Body of Knowledge, 4th Edition, Project management Institute Inc., 14 Campus Boulevard, Newton Square, Pennsylvania, 19073- 3299 USA

Heerkens, G.R. (2002). Project Management, The McGraw-Hill Companies, Inc. New York, Chicago, San Francisco, Lisbon, Madrid, Mexico City, Milan, New Delhi, San Juan, Seoul, Singapore, Sydney Toronto

Wysocki, R. K. (2009). Effective Project Management, Traditional, Agile, Extreme, 5th Edition, Wiley Publishing Inc., Indianapolis

Wysocki, R. K. (2006). Effective Software Project Management, Wiley Publishing Inc., Indianapolis

MADRAS (2008). PMP ® Exam Preparation Course, Project Scope Management [online] Available at  http://www.torrenthound.com/hash/c346d6be09ccf170ce591337472725c77f7c0d9c/torrent-info/PMP-4th-Slides-PDF  [Accessed: 28 March 2012]

MADRAS (2008). PMP ® Exam Preparation Course, Project Integration Management [online] Available at  http://www.torrenthound.com/hash/c346d6be09ccf170ce591337472725c77f7c0d9c/torrent-info/PMP-4th-Slides-PDF  [Accessed: 28 March 2012]

MADRAS (2008). PMP ® Exam Preparation Course, Project Time Management [online] Available at  http://www.torrenthound.com/hash/c346d6be09ccf170ce591337472725c77f7c0d9c/torrent-info/PMP-4th-Slides-PDF  [Accessed: 28 March 2012]