Waterfall Model / Classical Waterfall model

1.  It is the simplest software development model and was popularized in 1970s.
2. It is also known as Software life cycle.
3. According to Waterfall Model, Software development is structured into phrases, where output of one phrase is important and constitutes the next phrase.
4. All the phrases will function one after another in linear manner.

The stages/phrases in Waterfall Model are

1. Requirements Gathering 
2. System Analysis and Design
3. Coding
4. Testing
5. Integration and implementation
6. Operation & Maintenance 

1. Requirements Gathering 

In this stage, the software requirements (user requirements, system requirements, functional requirements) are identified and documented in detail. 

This stage involves a lot of communication with the customer.

2. System Analysis & Design

• At this step the developers decide a road map of their plan and try to bring up the best software model suitable for the project.
• The project team will analyze the software product limitations, problems and scope of the project and plans the schedule and resources accordingly. 
• After analysis, software architecture and design are created based on requirements gathered.
• The output of this step comes in the form of two designs i.e logical and physical designs. 
• Engineers prepare metadata, logical diagrams, data-flow diagrams and in some case pseudo codes.

Pseudo code is a detailed readable description of a computer program or algorithm must do, expressed in a formally styled natural language rather than in a programming language. Advertisement

3. Coding

• This phrase is also known as programming phrase.
• This phrase implement the software design in writing code in the suitable programming language and developing error free executable programs efficiently.

4. Testing 

• In this stage, the software is tested to identify and fix any defects or issues in the code. 
• The testing phrase may involve functional, performance, and security testing.

5. Integration and implementation 

• After coding and testing, software may need to be integrated with the libraries, databases, and other programs.
• This stage is involved in the Integration of software with outer world entities. 

6. Operation & Maintenance 

In this stage, the software is maintained and updated over time to ensure it continues to meet the needs of the end users. This phrase may involve bug fixes, updates, and enhancements to the software. 

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Advantages of Waterfall Model:

1. Simple and easy to understand & use
2. Clearly defined stages
3. Easy to arrange tasks
4. Works well for smaller projects where requirements are very well understood at the beginning. 
5. Process and results are well documented. 

Disadvantages of Waterfall Model:

1. It is difficult to define all requirements at the beginning of project.
2. This model is not suitable for accommodating any change. 
3. It involves heavy documentation.
4. There is no risk analysis.