Software Development Models

Evolutionary Model

Combination of iterative and incremental models.
Delivers the system incrementally over time.
Requires initial requirements and architecture envisioning.
Suited for products with feature sets that are redefined during development due to user feedback.
Divides development cycle into smaller, incremental waterfall models.
Users provide feedback on the product for the next cycle's planning stage.
The development team responds by changing the product, plan, or process.
The software product evolves with time.
Breaks down work into smaller chunks, prioritizes them, and delivers them to the customer one by one.
Customer's confidence increases with continuous delivery of quantifiable goods or services.
Allows for changing requirements.
All work is broken down into maintainable work chunks.
Used in large projects where modules for incremental implementation are easily found.
Commonly used when the customer wants to start using the core features instead of waiting for the full software.
Used in object-oriented software development because the system can be easily portioned into units in terms of objects.

Iterative (Water Fall) Model

Incorporates necessary changes to the classical waterfall model to make it usable in practical software development projects.
Provides feedback paths from every phase to its preceding phases.
Feedback paths allow for correcting errors committed by programmers during some phase.
The phase in which errors are committed can be reworked, and these changes are reflected in the later phases.
There is no feedback path to the stage – feasibility study.
It is good to detect errors in the same phase in which they are committed.
Reduces the effort and time required to correct errors.
Combines the sequential steps of the traditional Waterfall Model with the flexibility of iterative design.
Allows for improvements and changes to be made at each stage of the development process, instead of waiting until the end of the project.
Example: building a new website for a small business.

Incremental Process Model

Also known as the Successive version model.
First, a simple working system implementing only a few basic features is built and delivered to the customer.
Many successive iterations/versions are implemented and delivered to the customer until the desired system is released.
The requirement of Software is first broken down into several modules that can be incrementally constructed and delivered.
The plan is made just for the next increment and not for any kind of long-term plan.
It is easier to modify the version as per the needs of the customer.
The Development Team first undertakes to develop core features (these do not need services from other features) of the system.
Once the core features are fully developed, then these are refined to increase levels of capabilities by adding new functions in Successive versions.
Each incremental version is usually developed using an iterative waterfall model of development.

Advantages:

It is easier to test and debug during a smaller iteration.
Customer can respond to each built.
This model is less costly compared to others.
Initial product delivery is faster.

Disadvantages:

Needs good planning and design.
Needs a clear and complete definition of the whole system before it can be broken down and built incrementally.
More management attention is required.

Spiral Model

A Software Development Life Cycle (SDLC) model that provides a systematic and iterative approach to software development.
Looks like a spiral with many loops.
The exact number of loops of the spiral is unknown and can vary from project to project.
Each loop of the spiral is called a Phase of the software development process.
The exact number of phases needed to develop the product can be varied by the project manager depending upon the project risks.
The project manager has an important role in developing a product using the spiral model.
Based on the idea of a spiral, with each iteration of the spiral representing a complete software development cycle, from requirements gathering and analysis to design, implementation, testing, and maintenance.

Phases of Spiral Model:

Planning: The first phase where the scope of the project is determined and a plan is created for the next iteration of the spiral.
Risk Analysis: Risks associated with the project are identified and evaluated.
Engineering: The software is developed based on the requirements gathered in the previous iteration.
Evaluation: The software is evaluated to determine if it meets the customer’s requirements and if it is of high quality.

Advantages:

Risk Handling: The projects with many unknown risks that occur as the development proceeds, in that case, the Spiral Model is the best development model to follow due to the risk analysis and risk handling at every phase.
Good for large projects: It is recommended to use the Spiral Model in large and complex projects.
Flexibility in Requirements: Change requests in the Requirements at a later phase can be incorporated accurately by using this model.
Customer Satisfaction: Customers can see the development of the product at the early phase of the software development and thus, they habituated with the system by using it before completion of the total product.
Iterative and Incremental Approach: The Spiral Model provides an iterative and incremental approach to software development, allowing for flexibility and adaptability in response to changing requirements or unexpected events.
Emphasis on Risk Management: The Spiral Model places a strong emphasis on risk management, which helps to minimize the impact of uncertainty and risk on the software development process.
Improved Communication: The Spiral Model provides for regular evaluations and reviews, which can improve communication between the customer and the development team.
Improved Quality: The Spiral Model allows for multiple iterations of the software development process, which can result in improved software quality and reliability.

Disadvantages:

Complex: The Spiral Model is much more complex than other SDLC models.
Expensive: Spiral Model is not suitable for small projects as it is expensive.
Too much dependability on Risk Analysis: The successful completion of the project is very much dependent on Risk Analysis. Without very highly experienced experts, it is going to be a failure to develop a project using this model.
Difficulty in time management: As the number of phases is unknown at the start of the project, time estimation is very difficult.
Complexity: The Spiral Model can be complex, as it involves multiple iterations of the software development process.
Time-Consuming: The Spiral Model can be time-consuming, as it requires multiple evaluations and reviews.
Resource Intensive: The Spiral Model can be resource-intensive, as it requires a significant investment in planning, risk analysis, and evaluations.

Prototype Model

Prototyping is defined as the process of developing a working replication of a product or system that has to be engineered. It offers a small-scale facsimile of the end product and is used for obtaining customer feedback.
The Prototyping Model is one of the most popularly used Software Development Life Cycle Models (SDLC models). This model is used when the customers do not know the exact project requirements beforehand. In this model, a prototype of the end product is first developed, tested, and refined as per customer feedback repeatedly till a final acceptable prototype is achieved which forms the basis for developing the final product.
In this process model, the system is partially implemented before or during the analysis phase thereby giving the customers an opportunity to see the product early in the life cycle. The process starts by interviewing the customers and developing the incomplete high-level paper model.
This document is used to build the initial prototype supporting only the basic functionality as desired by the customer. Once the customer figures out the problems, the prototype is further refined to eliminate them. The process continues until the user approves the prototype and finds the working model to be satisfactory.

Steps to build Prototype Model

Step 1: Requirement Gathering and Analysis: This is the initial step in designing a prototype model. In this phase, users are asked about what they expect or what they want from the system.
Step 2: Quick Design: This is the second step in Prototyping Model. This model covers the basic design of the requirement through which a quick overview can be easily described.
Step 3: Build a Prototype: This step helps in building an actual prototype from the knowledge gained from prototype design.
Step 4: Initial User Evaluation: This step describes the preliminary testing where the investigation of the performance model occurs, as the customer will tell the strength and weaknesses of the design, which was sent to the developer.
Step 5: Refining Prototype: If any feedback is given by the user, then improving the client’s response to feedback and suggestions, the final system is approved.
Step 6: Implement Product and Maintain: This is the final step in the phase of the Prototyping Model where the final system is tested and distributed to production, here program is run regularly to prevent failures.

Advantages:

The customers get to see the partial product early in the life cycle. This ensures a greater level of customer satisfaction and comfort.
New requirements can be easily accommodated as there is scope for refinement.
Missing functionalities can be easily figured out.
Errors can be detected much earlier thereby saving a lot of effort and cost, besides enhancing the quality of the software.
The developed prototype can be reused by the developer for more complicated projects in the future.
Flexibility in design.
Early feedback from customers and stakeholders can help guide the development process and ensure that the final product meets their needs and expectations.
Prototyping can be used to test and validate design decisions, allowing for adjustments to be made before significant resources are invested in development.
Prototyping can help reduce the risk of project failure by identifying potential issues and addressing them early in the process.
Prototyping can facilitate communication and collaboration among team members and stakeholders, improving overall project efficiency and effectiveness.
Prototyping can help bridge the gap between technical and non-technical stakeholders by providing a tangible representation of the product.

Disadvantages:

Costly with respect to time as well as money.
There may be too much variation in requirements each time the prototype is evaluated by the customer.
Poor Documentation due to continuously changing customer requirements.
It is very difficult for developers to accommodate all the changes demanded by the customer.
There is uncertainty in determining the number of iterations that would be required before the prototype is finally accepted by the customer.
After seeing an early prototype, the customers sometimes demand the actual product to be delivered soon.
Developers in a hurry to build prototypes may end up with sub-optimal solutions.
The customer might lose interest in the product if he/she is not satisfied with the initial prototype.
The focus on prototype development may shift the focus away from the final product, leading to delays in the development process.
The prototype may give a false sense of completion, leading to the premature release of the product.
The prototype may not consider technical feasibility and scalability issues that can arise during the final product development.
The prototype may be developed using different tools and technologies, leading to additional training and maintenance costs.
The prototype may not reflect the actual business requirements of the customer, leading to dissatisfaction with the final product.