Constrains, its impact on Baseline and Delay analysis

Understanding Constraints in Baseline Scheduling

Effective project management often hinges on the careful use of constraints within baseline scheduling. Constraints can significantly impact how tasks are driven and sequenced. This discussion delves into the classification and implications of different constraints, focusing on their role in maintaining a logic-driven schedule.

Classification of Constraints

Constraints are typically divided into two main categories: Hard Constraints and Soft Constraints. This classification helps in identifying how different constraints influence task scheduling and overall project performance.

1.????? Hard Constraints

Hard Constraints impose strict conditions that affect both the forward and backward scheduling passes. These constraints can override logical sequencing, potentially leading to scheduling conflicts. For this reason, if more than 5% of the total tasks in a project have a Hard Constraint, the scheduling test is deemed to have failed.

Historically, the term "Hard Constraints" was not standardized in the industry. In the early versions of the Defense Contract Management Agency (DCMA) guidelines, Hard Constraints were defined by their impact on the scheduling passes. Specifically, they included constraints or combinations of constraints such as:

·?????? Start On or Before + Start On or After

·?????? Finish On or Before + Finish On or After

·?????? Must Start On

·?????? Must Finish On

The DCMA’s November 9, 2009 revision provided a more precise definition of Hard Constraints, categorizing them as:

·?????? Must-Finish-On (MFO)

·?????? Must-Start-On (MSO)

·?????? Start-No-Later-Than (SNLT)

·?????? Finish-No-Later-Than (FNLT)

These constraints enforce rigid deadlines or start times, making it difficult to adjust the schedule logically in response to project dynamics.

The key understanding is the hard Constraints that prevent activities from being rescheduled or moved.

?2.????? Soft Constraints

In contrast, Soft Constraints offer more flexibility. They are generally used to guide the schedule without enforcing absolute limits, thus allowing the schedule to remain largely logic-driven. According to the revised DCMA definitions, Soft Constraints include:

·?????? As-Soon-As-Possible (ASAP)

·?????? Start-No-Earlier-Than (SNET)

·?????? Finish-No-Earlier-Than (FNET)

These constraints provide guidelines rather than hard deadlines, ensuring that the project can adapt to changes while maintaining a coherent schedule.

The Soft Constraints that allow activities to be rescheduled or moved without restriction.

Implications for Baseline Scheduling

Understanding the types of constraints and their impacts is necessary for effective baseline scheduling. Hard Constraints should be used sparingly, as excessive reliance on them can disrupt the logical flow of tasks and lead to scheduling inefficiencies. On the other hand, Soft Constraints help maintain flexibility, ensuring that the project can adjust to unforeseen changes without compromising the overall schedule integrity.

Effective Use of Constraints in Baseline Preparation

The DCMA highlights that hard constraints can hinder the adjustment of tasks based on their dependencies, thereby compromising a logic-driven schedule. Conversely, soft constraints support the maintenance of a logic-driven schedule by allowing more flexibility in task adjustments.

While soft constraints are often overlooked, the current metric is somewhat lenient with hard constraints. It considers the schedule to fail only if the proportion of hard constraints exceeds 5% of the total activities. This threshold is surprisingly high, as even 5% of tasks with hard date constraints can significantly disrupt the schedule’s usability.

Focusing exclusively on hard constraints opens up considerable potential for logic abuse. Since the test only evaluates hard constraints, it is possible for every activity in the schedule to have an imposed constraint as long as it isn’t classified as hard. Furthermore, the metric only accounts for "Total Tasks," excluding milestones with hard constraints and focusing solely on activities with durations.

Limitations and Instability of the Metric

The metric also exhibits instability and a tendency to deteriorate over time. It tracks hard constraints relative to the total number of uncompleted tasks, which decreases as the project progresses. If hard constraints are used near the end of a project, this shrinking base number can turn a condition that once passed at 1% into a failing condition at 6%, even if the schedule is running as planned.

Additionally, this metric does not address the core issue of using constraints: they override calculated dates and interfere with the activity’s float value. The Critical Path Method (CPM) is designed to highlight critical tasks that must be completed on time for the project to meet its deadline. Constraints disrupt this process by imposing fixed dates that can conflict with the logical flow of the schedule.

Recommendations for Effective Constraint Use

To ensure a logic-driven and manageable baseline schedule, it is crucial to use constraints prudently:

·?????? Minimize Hard Constraints: Limit the use of hard constraints to essential situations where absolutely necessary. Over-reliance on hard constraints can lead to scheduling inflexibility and potential project delays.

·?????? Document Constraints Clearly: Clearly document the rationale for each hard constraint. This transparency helps in understanding the necessity and impact of each constraint.

·?????? Prioritize Soft Constraints: Use soft constraints wherever possible to maintain flexibility. Soft constraints allow the schedule to adapt to changes without disrupting the logical sequence of tasks.

·?????? Regularly Review and Adjust: Continuously review the constraints applied throughout the project lifecycle. Adjust constraints as needed to ensure they align with the project’s evolving requirements and conditions.

·?????? Ensure Comprehensive Testing: Test the schedule under various scenarios to ensure that constraints are not unduly affecting the critical path and that the schedule remains logic-driven.

Constraints undoubtedly complicate analysis but do not render it impossible. It is important to remember that constraints were initially imposed to facilitate schedule development. Each constraint serves a specific purpose, representing essential logic for the accurate modeling of the plan. Refer to the FSA RP, Section 2.1, Baseline Schedule Selection, Validation, and Rectification (SVP 2.1), C. Recommended Enhanced Protocol, particularly:

Bullet 3: "Document the basis of all controlling and non-controlling constraints."

Bullet 4: "Replace controlling constraints, except for the start and finish milestones, with logic and/or activities."

?The first step is to systematically replace the constraints. I approach this by making changes one at a time and comparing the results before and after each modification. This helps identify the impact of constraints on the contemporaneous reporting of the Critical Path.

In the case of soft constraints, the controlling aspect is often straightforward and may not have been violated. When a violation does occur, it is crucial to understand the potential consequences. Replacing constraints and reviewing the outcomes is simpler than retaining the constraints and attempting to analyze negative float issues.

For instance, if a constraint involves access to perform work within a railroad right-of-way (ROW) and access was denied, replacing the constraint with logic and recalculating can reveal that the project was delayed solely due to the constraint violation. This process provides clarity on both the extent of the delay and the responsibility for it. Analyzing constraints individually in this manner enhances understanding and supports robust analysis conclusions.

Although replacing all constraints may seem daunting, it is the most effective approach for comprehensive analysis. This method also strengthens the credibility of your conclusions.

The choice of methodology should follow standard practice; there is no single superior method for handling constraints. Observational methods, which do not require schedule recalculations after adding activities, can be less complex compared to modeled methods. The necessity of recalculating schedules after incorporating fragnets complicates the use of modeled methods with constraints.