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Dependency Determination and Types in CPM

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In the context of the Critical Path Method (CPM), defining and analyzing dependencies between project activities is a fundamental step in constructing an accurate project schedule. Dependencies dictate the sequence in which tasks are performed and influence the timing relationships between activities. Properly identifying and implementing dependencies ensures logical workflow and allows for effective management of project timelines. There are four primary types of activity dependencies: 1. **Finish-to-Start (FS)**: The successor activity cannot start until the predecessor activity has finished. This is the most common dependency type and represents a typical sequential relationship. For example, you cannot begin painting a wall (successor) until the wall has been constructed (predecessor). 2. **Start-to-Start (SS)**: The successor activity cannot start until the predecessor activity has started. This dependency is used when two activities can occur in parallel after both have begun. For instance, once design work starts, coding can commence, allowing for overlapping work. 3. **Finish-to-Finish (FF)**: The successor activity cannot finish until the predecessor activity has finished. This relationship is used when the completion of one task is contingent upon the completion of another. For example, editing a document cannot be completed until writing the document is finished. 4. **Start-to-Finish (SF)**: The successor activity cannot finish until the predecessor activity has started. This is the least common type and is used in scenarios where the successor must continue until the predecessor begins. An example might be a night shift guard (successor) cannot finish duty until the day shift guard (predecessor) arrives. Dependencies can also be categorized based on their nature: - **Mandatory Dependencies**: These are inherent in the nature of the work and are often contractually or physically required. They represent hard logic. For example, you must receive approval before you can proceed with procurement. - **Discretionary Dependencies**: Also known as soft logic, these are defined by project teams based on best practices or preferences. They offer flexibility in sequencing and can be adjusted to compress schedules if necessary. - **External Dependencies**: Dependencies that involve relationships between project activities and non-project activities, which are outside the project team's control. For example, waiting for government permits. Understanding and accurately modeling these dependencies is crucial for constructing the project’s schedule network diagram. It ensures activities are logically sequenced, resource allocations are optimized, and potential scheduling conflicts are minimized. Dependencies affect the calculation of early start (ES), early finish (EF), late start (LS), and late finish (LF) dates during the forward and backward pass techniques in CPM. Incorrect dependency determination can lead to flawed critical path identification, resulting in schedule delays, resource bottlenecks, and cost overruns. Effective dependency management enhances project control by providing clarity on task relationships, facilitating communication among stakeholders, and allowing for proactive risk management. It enables project managers to foresee the impact of changes in one activity on the rest of the schedule and adjust plans accordingly to maintain project objectives.

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Question 1

In a Critical Path Method (CPM) analysis, what best describes a mandatory dependency (also known as hard logic)?

Correct Answer: A relationship inherently required by the physical nature of the work

A mandatory dependency or hard logic in CPM represents relationships between activities that are physically impossible to break or change due to the inherent nature of the work. For example, you cannot paint a wall before constructing it, or pour concrete before setting up the formwork. These are physical limitations that cannot be changed regardless of preference or circumstances. The other options are incorrect because: - Best practices and preferred implementation sequences describe discretionary dependencies (soft logic), which are based on preferences rather than physical necessities - Organizational policies and historical patterns refer to external dependencies that are imposed by organizational procedures - Market conditions and resource constraints describe external dependencies that are based on factors outside the project's physical requirements

Question 2

Which of the following best describes a logical relationship in a CPM network where one activity must be delayed by a specific duration after another activity starts?

Correct Answer: Start-to-Start (SS) with lag

In CPM network diagrams, a Start-to-Start (SS) with lag relationship indicates that there must be a specified time delay between the start of one activity and the start of its successor activity. This is precisely what the question asks for - a relationship where one activity must be delayed by a specific duration after another activity starts. The other options are incorrect because: Parallel paths with positive float time refers to schedule flexibility, not a mandatory delay requirement. Start-to-Finish (SF) with negative lag is rarely used in practice and describes a relationship where a successor activity must finish a certain duration after the start of its predecessor. Finish-to-Start (FS) describes a sequential relationship where an activity starts after its predecessor finishes, not a delay from the start of an activity.

Question 3

In a Critical Path Method (CPM) network diagram, which statement best describes a Finish-to-Start (FS) dependency relationship?

Correct Answer: The successor activity can start only after the predecessor activity has finished

A Finish-to-Start (FS) dependency is the most common relationship in project scheduling. In this relationship, the successor activity can only begin after its predecessor activity has completed. This is logical because many project activities require the completion of previous work before new work can begin. For example, you need to complete the foundation before starting to build walls. The other options are incorrect because: - Starting activities at the exact same time describes a Start-to-Start (SS) relationship, not an FS - Having the successor finish before the predecessor starts would create an illogical backwards relationship - The 5-day lag requirement is arbitrary and not a characteristic of FS relationships - lags can be any duration and are optional in FS relationships

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