Let's look closer at the difference between Agile and Waterfall methodologies.

In management, there is a concept of a project management triangle14:

It includes the amount of work, time and quality. It is important to note that the balance in any methodology is created due to a system of assumptions, so in cascade approach quality can be reduced, and in Agile the amount of work can easily grow.

The project management triangle clearly displays the so-called triple limitation problem associated with the need to balance the scope of the project, its cost and time for implementation without compromising the quality of the final product. Taking into consideration the concept of project management triangle, the difference between approaches will look like this:

In recent years, the waterfall model has been losing its leading position to more flexible methodologies. This is due to the general dynamics in IT, when teams of 5-9 people are responsible for software development, and the deadline can be easily shifted due to the increase in functionality.

Nevertheless, the cascade model is still relevant for large projects and organizations:

• It is resistant to personnel changes. Developers can come and go throughout the life cycle of the project, but thanks to detailed documentation, this practically does not affect the timing of the project;

• Waterfall model forces developers involved in the project to be disciplined and to stay within the plan. If necessary, a management body responsible for decision-making is added to the general model, while performers are required to work within the system framework15;

• Flexibility in the early stages. Changes in early phases can be made immediately and with minimal effort, since they are not backed up by code. Thus, the customer and the contractor have a significant time margin for a radical change in the concept of software work;

• Focus on deadlines and finances. Due to the fact that each stage completely outlines the contour of the future software, all developers understand their role, the boundaries of work and deadlines. This allows you to cooperate with the customer knowing the real cost of development and makes, therefore, the project model attractive.

In the 1970s, Royce's ideas were relevant. But after almost 50 years, the cascade development method is less and less suitable for IT:

• non-adaptive software structure. At the first stages, the waterfall model can be flexible, but if problems in the overall structure are identified during the testing phase, this entails deplorable consequences in the form of disrupted deadlines and even customer failures;

• ignores the end user. The lower the process progresses in the waterfall, the less the role of the customer in it, not to mention the users he represents. Making any changes to the functionality of the software starts the entire chain of stages anew, so the products obtained by the cascade model are far from targeting the mass user;

• later testing. It is here that mistakes made at each of the stages are most often identified. More flexible methodologies use testing as a fundamental operation that occurs continuously. Waterfall, on the other hand, admits low qualifications of employees at each stage and poor quality of execution, because with late testing, problems cannot be solved fundamentally, only with the help of "patches".

Let's fix both approaches pros and cons:

Everything seems to be transparent, but in practice the question often arises which methodology to apply in each specific case. This scheme helps us mostly to make the right choice: