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A Simulation Model for the Waterfall Software Development Life Cycle
Youssef Bassil
TL;DR
Software projects face delays, cost overruns, and delivery problems associated with inadequate resource allocation across SDLC activities. This paper models the Waterfall process in Simphony.NET to determine resource requirements and balance project arrivals with deliveries. The simulation delivered 50 of 50 projects and identified resource requirements for the Waterfall phases, while future work extends the approach to other SDLC models.
Problem
Inadequate assignment of workers and resources across SDLC activities can delay phases, idle dependent resources, and create project-delivery bottlenecks.
Method
The paper builds and integrates a Simphony.NET simulation of Waterfall phases, resources, tasks, workflows, project scales, and project arrivals and deliveries.
Results
50 projects were delivered out of 50, and the simulation identified optimal numbers of analysts, designers, programmers, testers, and maintenance workers.
Takeaways & Limitations
The model assists project managers in determining resource requirements for producing particular software solutions within schedule and budget constraints.
Takeaways & Limitations
The study’s future work is to simulate other SDLC models, including spiral and incremental approaches.
Abstract
from arXiv · showhide
Software development life cycle or SDLC for short is a methodology for designing, building, and maintaining information and industrial systems. So far, there exist many SDLC models, one of which is the Waterfall model which comprises five phases to be completed sequentially in order to develop a software solution. However, SDLC of software systems has always encountered problems and limitations that resulted in significant budget overruns, late or suspended deliveries, and dissatisfied clients. The major reason for these deficiencies is that project directors are not wisely assigning the required number of workers and resources on the various activities of the SDLC. Consequently, some SDLC phases with insufficient resources may be delayed; while, others with excess resources may be idled, leading to a bottleneck between the arrival and delivery of projects and to a failure in delivering an operational product on time and within budget. This paper proposes a simulation model for the Waterfall development process using the Simphony.NET simulation tool whose role is to assist project managers in determining how to achieve the maximum productivity with the minimum number of expenses, workers, and hours. It helps maximizing the utilization of development processes by keeping all employees and resources busy all the time to keep pace with the arrival of projects and to decrease waste and idle time. As future work, other SDLC models such as spiral and incremental are to be simulated, giving project executives the choice to use a diversity of software development methodologies.
1. INTRODUCTION
Software development methodologies organize the planning, management, and control of information-system development through sequential phases. The paper proposes a Simphony.NET simulation to identify resource levels that improve Waterfall productivity while minimizing workers, time, and budget.
- SDLC is a framework for planning, managing, and controlling information-system development across engineering and industrial fields.
- Waterfall firms often assign dedicated expert departments to analysis, engineering, programming, quality assurance, and technical support phases.
- Appropriate resource assignment across Waterfall phases remains difficult because managers must balance people, equipment, processes, time, effort, and budget.
- Computer simulation can model an abstract system to discover behavior, estimate outcomes, and analyze operations.
- The proposed Simphony.NET model represents Waterfall stakeholders, phases, tasks, workflows, project scales, arrivals, deliveries, and resource utilization.
- The simulation seeks optimal resource levels that keep incoming projects flowing with minimal workers, time, and budget.
2. THE WATERFALL SDLC MODEL
The Waterfall SDLC is a sequential process in which five phases are completed in order, with each phase defining a distinct development responsibility. The phases span requirements analysis, design, implementation, testing, and post-delivery maintenance.
- The Waterfall model requires consecutive phases to be completed one after another before progress moves forward.
- The model comprises five phases: analysis, design, implementation, testing, and maintenance.
- Analysis Phase: Analysis produces a Software Requirements Specification describing the software’s functional and non-functional requirements.
- Design Phase: Design plans the software solution through algorithms, architecture, databases, interfaces, concepts, and data structures.
- Implementation Phase: Implementation converts requirements and design specifications into executable programs, databases, websites, or software components.
- Testing Phase: Testing verifies that phase products satisfy imposed conditions and validates that the software meets requirements and intended purposes.
- Maintenance Phase: Maintenance modifies deployed software to correct errors, improve performance and quality, adapt to its environment, and accommodate new requirements.
3. RELATED WORK
Related work applies simulation to software development planning, small-scale process modeling, facilitation, and life-cycle reliability evaluation. These approaches differ in scope, purpose, and the stages or processes they represent.
- Simulation planning can precede development by defining the project structure, simulation scope, and use of results for future planning.
- Simulation as facilitation uses small-scale models to support understanding and debate about problem situations.
- A system-dynamics facilitation model represents conceptualization, development, and group learning around findings and recommendations.
- A software-development life-cycle simulation guideline includes ten processes, ten phases, and thirteen reliability evaluation stages.
4. PROBLEM DEFINITION & MOTIVATIONS
Software projects experience delays, cost overruns, postponed deliveries, and occasional failures, while poor resource allocation creates delays, idle dependent phases, and delivery bottlenecks. The proposed Waterfall simulation targets trade-offs among cost, schedule, functionality, and resource utilization.
- Software development projects have encountered delays, cost overruns, postponed deliveries, dissatisfied customers, and occasional total failures.
- Insufficient workers can delay some SDLC phases while dependent phases remain idle awaiting completion.
- These phase imbalances create bottlenecks between project arrival and delivery, undermining timely, budgeted, and functional-product delivery.
- The simulation seeks trade-offs among cost, schedule, and functionality while keeping employees and resources utilized and reducing waste and idle time.
5. THE SIMULATION MODEL
The model represents Waterfall phases, resources, workflows, project scales, arrivals, and phase errors in Simphony.NET, then iteratively simulates and integrates them to identify resource needs.
- The simulation targets matching project arrivals and deliveries while minimizing idle and busy resources, workers, time, and budget.
- The modeling procedure divides Waterfall into phases, defines each phase’s resources and workflow, simulates phases separately, and then integrates the full system.
- Assumptions and Specifications: Phase durations use Uniform distributions: business analysis 3–5 days, design 5–10, implementation 15–20, testing 5–10, and maintenance 1–3.
- The Simphony Model: Simphony.NET models employees, queues, tasks, probability branches, captures, releases, counters, project entities, and Waterfall phases.
- Running the Simulation: Across five runs with 50 incoming projects, the model delivered 50 projects and estimated optimal staffing of 5.2 analysts, 11.6 designers, 21.02 programmers, 7.4 testers, and 2.09 maintenance workers.
6. CONCLUSIONS & FUTURE WORK
The proposed Simphony.NET model simulates the Waterfall life cycle and its entities to help project managers determine optimal resources within schedule and budget constraints. Experiments found it accurately calculated required resources using utilization metrics, while future work extends simulation to spiral and incremental models.
- The model simulates Waterfall entities, including software solutions, operational resources, employees, tasks, and phases.
- Experiments showed accurate calculation of optimal resources required for a software solution based on resource utilization.
- Future work will simulate spiral and incremental SDLC models, allowing project managers to choose among more development methodologies.