Opposite branch of tashkent university of information technologies named muhammad al-khorazmi

Waterfall Model
The waterfall model is a sequential, plan driven-process where you must plan and schedule all your activities before starting the project. Each activity in the waterfall model is represented as a separate phase arranged in linear order.
It has the following phases:

• 
  Requirements
  
• 
  Design
  
• 
  Implementation
  
• 
  Testing
  
• 
  Deployment
  
• 
  Maintenance
  

Each of these phases produces one or more documents that need to be approved before the next phase begins. However, in practice, these phases are very likely to overlap and may feed information to one another.
The software process isn’t linear, so the documents produced may need to be modified to reflect changes.
The waterfall model is easy to understand and follow. It doesn’t require a lot of customer involvement after the specification is done. Since it’s inflexible, it can’t adapt to changes. There is no way to see or try the software until the last phase.
The waterfall model has a rigid structure, so it should be used in cases where the requirements are understood completely and unlikely to radically change.

V Model
The V model (Verification and Validation model) is an extension of the waterfall model. All the requirements are gathered at the start and cannot be changed. You have a corresponding testing activity for each stage. For every phase in the development cycle, there is an associated testing phase.
The corresponding testing phase of the development phase is planned in parallel, as you can see above.
The V model is highly disciplined, easy to understand, and makes project management easier. But it isn’t good for complex projects or projects that have unclear or changing requirements. This makes the V model a good choice for software where downtimes and failures are unacceptable.

Incremental Model
The incremental model divides the system’s functionality into small increments that are delivered one after the other in quick succession. The most important functionality is implemented in the initial increments.
The subsequent increments expand on the previous ones until everything has been updated and implemented.
Incremental development is based on developing an initial implementation, exposing it to user feedback, and evolving it through new versions. The process’ activities are interwoven by feedback.
Each iteration passes through the requirements, design, coding, and testing stages.
The incremental model lets stakeholders and developers see results with the first increment. If the stakeholders don’t like anything, everyone finds out a lot sooner. It is efficient as the developers only focus on what is important and bugs are fixed as they arise, but you need a clear and complete definition of the whole system before you start.
The incremental model is great for projects that have loosely coupled parts and projects with complete and clear requirements.