Project Management Dependency Flashcard
Wysocki (2009, p.161) defines a project network diagram as a “pictorial representation of the sequence in which the project work is done”. They are logically arranged, and are used for detailed project planning and also used as control tools. Precedence Diagramming Method (PDM), is the most commonly used method for developing a project network diagram with each task being represented by a rectangle and arrows representing both predecessor and successor relationships between tasks. Wysocki (2009, p.165) describes dependency as a relationship that exists between tasks. Dependencies are important in the development of a network diagram.
It helps to determine predecessors and successors for each task. When an output is achieved on the completion of a task, these outputs now become inputs to its successor task. Wysocki (2009, p.164), states that “work on the successor tasks requires only the output from its predecessor tasks”. As explained by Franchina (2010), task dependencies helps project managers determine methodologies that are needed to estimate task duration and know best approaches towards the project schedule and identify tasks that have potential to skew the project schedule. Wysocki (2009, pp. 166-167) gives four types of dependencies.
1. Finish-to-Start (FS): Task (A) must end before task (B) can start. For example, in the installation of a Vsat, A pole is meant to be erect (A) before the Vsat is mounted on it (B). 2. Start-to-Start (SS): Task B can start once task (A) starts. An example by Biafore (n.d.) is, “Members of a road construction crew starts to place traffic cones to close a lane on the highway (A). Ten minutes after they start, the line-painting machine starts to paint lines (B). 3. Start-to-Finish (SF): Task (B) can’t finish Before Task (A) starts. Deng (2011) gives us an example when he states that “our developer couldn’t finalize the layout for the homepage without first receiving graphics assets from our designer.” 4. Finish-to-Finish (FF): One task continues as long the other task is on. Task (B) can’t finish before task (A) is finished. Traffic flaggers’ direct traffic until construction work is complete.
Because they are least complex, Wysocki (2009, p.167) advices for the use of Finish-to-Start (FS) at the begining of the construction of a project network diagram. Biafore (n.d.) guides us in choosing the right dependency type by following these simple steps which helps to identify which tasks are in control and to identify the characteristics of the dependency needed.
1. Identify the predecessors to the task which is achieved by asking oneself, “what does this task need before it can start?” It helps to determine tasks that are predecessors to the task being evaluated. 2. Determine whether the start or finish of the predecessor controls the scheduling of the successor. For example, FF or FS is used if the completion of the predecessor controls the second task. 3. Determine whether the predecessor triggers the start of finish of the successor For instance, if the result of the previous step is finish and result for this step is start, the dependency type is FS. 4. Identify whether the dependency uses a lead or lag time which is based on the duration of the predecessor task. Dependencies are determined by existing constraints between tasks thus, they affect the task schedule by defining the relationship between tasks.
A Constraint is anything that prevents the project from achieving its goal. Wysocki (2009, p.167) identifies four constraints which would affect the sequencing of project tasks and dependency relations between the tasks.
1. Technical Constraints occurs because a task requires an output from its predecessor before work can begin on it. In the installation of a ground mount V-sat, a hole must be dug (task 1), a pole erected in it (task 2), concrete poured and left to set (task 3), before the v-sat is now mounted on the pole (task 4). Here, a Finish-to-Start (FS) dependency is used in this case because the completion of a predecessor task determines when the next task can begin. According to Wysocki (2009, pp.167-169) Technical constraints can be subdivided into (i) Judgment calls which is a decision a project manager takes to modify the sequences of a task. When ahead of schedule in the installation of the V-sat, and there is a risk of rain or strong winds, I can relocate my workmen to another task like the indoor cabling and wiring so as to prevent the V-sat from being blown off or the concrete from being washed off. (ii)Best-Practice constraints where I use my own personal experiences from similar tasks to adjust a schedule. I could split my workers into two sets and make one set mount the V-sat and the other set do all necessary wiring at the same time. (iii) Logical constraints where I use my own reasoning to find how to optimize project schedule. (iv) Unique requirements like regulatory inspections and specialized equipment affect successor tasks.
2. Management Constraints is a reversible constraint and is management-imposed. Tasks and schedules can be changed at anytime by the project manager to suit certain condition.
3. Inter project constraints occurs when deliverables from one project is needed in another project Wysocki (2009, pp.169-170). An example given in the construction of the Boeing 777 where different projects to manufacture different parts of the plane were done at different geographical locations by different facilities but had to be coordinated with the final assembly project plan.
4. Date constraints The dates for the begining and the end of tasks and projects are imposed before the project kicks off. These dates are mostly imposed by clients. Wysocki (2009, p. 170) states the three types of date constraints. (i) No earlier than- which specifies the earliest date a task would be completed. E.g, The v-sat installation would be through as from 5th of April. (ii) No later than- specifies a date a task must be completed. E.g, The v-sat installation would be through before 5th of April. (iii) On this date- Here a date is set in which the task must be completed. E.g, The v-sat installation must be through by 5th April.
Franchina (2010) explains that the process of establishing task dependencies is “Crucial in understanding the dynamics of a project and the development of a functional project management schedule”. And he cites (Cheng, Choi, Lee and Wu (1999)) where they warn that one must be cautious with potentially being redundant in using constraints and therefore, a need to review the network diagram as a whole and make necessary adjustments.