Spiral, Incremental, and Prototyping SDLC Models

Incremental Development Phases

Starting point: Definition of all requirements, general and preliminary project. This involves the choice of a subset of the system’s functions, followed by the detailed project and implementation of the system’s part implementing those chosen functions. Finally, testing of the completed part of the system and delivery to the client occurs, followed by a repetition of the process.

The Spiral Model Methodology

Planning and Objective Setting

Specific objectives for that phase of the project are defined. Constraints on the process and the product are identified, and a detailed management plan is drawn up. Project risks are identified, and alternative strategies may be planned.

Risk Analysis and Reduction

For each identified risk, a detailed analysis is carried out to ensure the reduction of risk. This phase can include prototype building.

Construction and Development

A development model for the system is chosen, followed by the choice of the system development model.

Testing and User Evaluation

The project is reviewed, and a decision is made whether to continue with a further loop of the spiral.

Prototyping and Implementation Workflow

• General requirements definition
• Prototype construction
• Prototype verification by the client
• Full requirements definition
• Full system realization according to the waterfall model
• Requirements definition
• Preliminary implementation
• User’s check
• Improvement in many versions until the final system is reached

Advantages and Disadvantages of SDLC Models

Incremental Model Analysis

Advantages:

• Frequent contact with the user
• Not necessary to define all requirements at the beginning
• Early use of the system by the client
• The first increment fulfills the most important requirements
• Possible to use the system early

Disadvantages:

• Small increments
• Every increment should deliver some functionality
• Additional cost of skeleton implementation
• Risk of no detection of some bugs during the testing phase

Spiral Model Analysis

Advantages:

• Explicit risk inclusion
• Risk decrease
• User evaluation and feedback

Disadvantages:

• Useful for systems which can be implemented with partial functionality and decreased quality
• Long time to reach the final version

Throwaway Prototyping Analysis

Note: These advantages are also useful for evolutionary models.

Advantages:

• Ability to demonstrate a quickly working version of the system
• Possibility of training before the system is ready

Disadvantages:

• Additional cost of prototype construction
• Potential astonishment of the client regarding the time and cost of prototype creation compared to the full system