The Waterfall Approach: Structure, Strengths, and Use Cases

UPI Study › Courses › Software Engineering › Free lessons › Lesson 1.9 Free with a free account

The Waterfall Approach: Structure, Strengths, and Use Cases

Software Engineering · Chapter 1: Foundations of Software Engineering and Process ModelsSection 1.9 · lesson 9 of 1036 min · free with a free account

← Common Misconceptions in Software EngineeringNext lesson: Recognizing Process Patterns Across Engineering Workflows →

Earn 3 college credits for Software EngineeringRecommended for credit by NCCRS · Computer Science 301 · self-paced · one payment, lifetime access
Enroll in Software Engineering · $250 →Download the syllabus (PDF)

In this lesson

Its origin, its sequential structure, its strengths and weaknesses, and where it still fits.

  • Explain where the waterfall approach and its name came from
  • Describe its sequential phases and phase gates
  • Weigh its strengths and weaknesses
  • Judge when it still makes sense today

Transcript

Everything said in the video, section by section (816 words). Read along, or search it.

Foundations of Software Engineering and Process Models

The Waterfall Approach

Figure out what is needed, design it, build it, test it, and ship it, in that order, each step finished before the next. That is the picture of software development most people already carry. It has a name, the waterfall approach. This section covers its surprising history, its structure, its strengths and weaknesses, and the narrower set of situations where it really works.

Where It Came From

A Diagram That Outlived Its Caveat

The waterfall approach is one of the earliest formal descriptions of the software process. It traces back to a widely cited nineteen seventy paper by Winston Royce, describing how large systems were being built at the time. And there is a well-known irony. Royce's paper is often credited with introducing the strictly sequential picture. But the paper itself warned that building a large system in one uninterrupted pass was risky. Royce argued for looping back, and revising earlier work as problems surfaced. The simplified, purely sequential version is what caught on, in practice and in teaching. What stuck was the diagram, not the caveat. Today, waterfall means one pass, in order, with no looking back.

The Structure

One Phase at a Time, Downhill

The name comes from the way the approach is drawn. A column of phases, each flowing down into the next, the way water falls from one level to the one below. Requirements come first, then design, then construction, then verification, and then maintenance once the system is in use. Each phase is completed, and signed off, before the next one begins.

Phase Gates

Deliverables and Sign-Offs

Each phase produces a defined set of deliverables, which becomes the starting point for the phase after it. A requirements document, then a design specification, then working code, then a test report. What makes the structure distinct is the discipline around moving between phases. Advancing requires a sign-off. The requirements are reviewed and approved before design starts, the design is approved before construction starts, and so on. Going backward is treated as an exception to be managed, not a routine part of the process. Discovering during construction that a requirement was wrong, means undoing work that later phases assumed was finished and correct.

Strengths

What a Rigid Process Buys

A process this rigid has real advantages. Clear milestones and deliverables make planning, budgeting, and scheduling straightforward, because the full scope is defined before work begins. The heavy documentation trail at each sign-off supports audits, and regulatory review, in industries where that trail is required. And it is easy to explain to stakeholders unfamiliar with software. The plan reads like a simple checklist, in order.

Weaknesses

What It Costs

Those advantages come with equally real costs. Working software is not visible until late in the process, so a wrong assumption often is not discovered until testing. Revisiting an earlier phase is costly, and treated as an exception, even though requirements commonly do shift. And the approach assumes requirements can be fully known up front, which is rarely true for unfamiliar or exploratory problems. The strengths and weaknesses share one root cause. Everything assumes the requirements were correct and complete at the very start. When they are, the predictability is a genuine asset. When they are not, the same rigidity that made planning easy makes correcting course expensive.

When It Still Fits

Stable, Specified, Audited

Waterfall fits best when a problem is well understood before work starts, and unlikely to change while the system is built. That tends to be true for systems built against fixed regulatory or safety standards, such as some medical device software, or embedded firmware. There, the requirements are dictated by an external specification, rather than discovered along the way. It also fits fixed-price government or defense contracts, where a formal, auditable trail between phases is part of what the contract requires. It fits poorly for products still being discovered, like a new consumer app where nobody yet knows what users really want. Many teams borrow pieces of waterfall, such as clear deliverables and formal sign-off, inside a larger project. But that kind of blending is a different approach, not waterfall itself.

Key Terms

The Vocabulary of This Section

Let's lock in the key terms. The waterfall approach is a fixed sequence of phases, each completed and formally signed off before the next begins. A phase gate is a formal review and approval point between phases. Verification is the phase that checks the completed system against its requirements and design. And requirements volatility is the tendency of requirements to change as a project proceeds. It is the central risk a strictly sequential approach is least equipped to absorb.

Key Takeaways

What to Carry Forward

To pull this together. The waterfall approach is named for its downward staircase of phases, and traces to Royce in nineteen seventy, who actually warned against a single rigid pass. Each phase produces a deliverable, and passes a sign-off, before the next begins. Its strengths, predictability, audit trails, and simplicity, all rest on the requirements being right from the start. Its weaknesses are late visibility of working software, and costly backtracking when requirements shift. And it still fits stable, externally specified, audited work, while fitting poorly for products still being discovered.

About Software Engineering at UPI Study

Software Engineering (Computer Science 301) is a self-paced online course of 103 video lessons in 15 chapters, from process models and agile to requirements, design, user interfaces, reliability, security and project management. It carries a NCCRS credit recommendation for 3 semester credits.

Every lesson transcript is free on pages like this one, and the videos are free with a free UPI Study account. Enrolling adds a practice quiz after each lesson, the graded work and final exam that earn the credit, lifetime access, and an official transcript on completion. UPI Study has helped over 130,000 students with college credits. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.

Enroll now → Course details Download the syllabus All Computer Science courses Every course with PRO →

Compare: Software Engineering vs Systems Analysis

Why take it here

Why students take Software Engineering with UPI Study

How professional software gets builtSoftware Engineering covers how teams turn requirements into working, maintainable software: process models, agile, requirements, design, testing, reliability and project management. It is a core course in computer science and software degrees.
Credit at a fraction of the priceThe same 3 credits can cost $750 or more at a US college. Here it is one payment, self-paced, with lifetime access.
Finish your degree soonerTransfer credits reduce the courses you still owe, so you can graduate earlier or lighten a heavy semester.
Strengthen an applicationA completed college-level course on an official transcript shows admissions and scholarship committees you can do the work.
Study on your own scheduleNo start dates, no deadlines. Watch the lessons, practice, and take the final when you are ready.
130,000+students helped with college creditsACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.

Where the credit goes

Universities that work with NCCRS

Software Engineering carries a NCCRS credit recommendation. These universities work with NCCRS; some are UPI Study's signed partners. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.

Thomas Edison State UniversityThomas Edison State UniversitySigned partnerUniversity of the PeopleUniversity of the PeopleSigned partnerCharter Oak State CollegeCharter Oak State CollegeSigned partnerStrayer UniversityStrayer UniversitySigned partnerColumbia Southern UniversityColumbia Southern UniversitySigned partnerIndiana TechIndiana TechSigned partnerPenn StatePenn StateWorks with NCCRSSouthern New Hampshire UniversitySouthern New Hampshire UniversityWorks with NCCRSSUNYSUNYWorks with NCCRS +many more cooperating universitiesFind my college →

Find my college → Not listed? Ask Athena in the corner of this page, or book a 15-minute call.

FAQ

Questions students ask us

About The Waterfall Approach: Structure, Strengths, and Use Cases

What is the waterfall model in software engineering?
The waterfall model is a fixed sequence of phases, each completed and formally signed off before the next begins. Requirements come first, then design, construction, verification and maintenance once the system is in use. Each phase produces a deliverable, such as a requirements document, design specification, working code or test report, which becomes the starting point for the phase after it.
Who created the waterfall model?
The waterfall approach traces back to a widely cited 1970 paper by Winston Royce describing how large systems were being built. Ironically, Royce warned that building a large system in a single uninterrupted pass was risky and argued for looping back to revise earlier work. The simplified, strictly sequential diagram is what caught on in practice and teaching, while his caveat was largely forgotten.
What are the advantages and disadvantages of the waterfall model?
Waterfall's advantages are clear milestones that make planning, budgeting and scheduling straightforward, a documentation trail that supports audits and regulatory review, and a plan that non-technical stakeholders can follow easily. Its disadvantages are that working software appears late, revisiting earlier phases is costly, and it assumes requirements are fully known up front. Both sides rest on the requirements being correct from the start.
When should you use the waterfall model?
Use waterfall when a problem is well understood before work starts and unlikely to change during the build. Examples include some medical device software or embedded firmware built against fixed regulatory or safety standards, and fixed-price government or defense contracts that require a formal, auditable trail between phases. It fits poorly for products still being discovered, such as a new consumer app.

About the Software Engineering course

How many college credits is Software Engineering?
Software Engineering (Computer Science 301) carries a NCCRS credit recommendation for 3 semester credits. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities.
How much does Software Engineering cost and what is included?
$250, paid once, with lifetime access: all 103 video lessons, a practice quiz after each, the graded work and final exam, and an official transcript when you finish. Students who want several courses choose UPI Study PRO instead.
Which universities accept UPI Study credits?
UPI Study has signed partner agreements with universities such as Thomas Edison State University, University of the People and Charter Oak State College, and works with universities such as Penn State, SNHU and SUNY. ACE and NCCRS have over 2,100 cooperating colleges that will consider accepting credits; the final decision is with the universities. Use "Find my college" on this page to check yours.
How long does Software Engineering take?
It is self-paced with no deadlines. The 103 lessons total about 11 hours of video; most students add reading and practice time and finish in a few weeks to a few months, on their own schedule.
How are the exams done?
Quizzes and assignments are online in the course. The final exam is taken online with proctoring; a person on the UPI Study team checks assignments, usually within two days.
How do my credits reach my college?
When the course shows 100% complete, request the official transcript from your dashboard. It is sent to the college you name, and you can send it to more than one. Check your college first with "Find my college" on this page, or ask Athena.

Ready for the full course? Earn 3 credits in Software Engineering.

103 video lessons, a quiz after each one, and the graded work that earns the credit. Recommended for credit by NCCRS.

Enroll in Software Engineering →Download the syllabusEvery course with PRO →
Software Engineering
3 credits · NCCRSEnroll →