The Waterfall, Iterative, and Ad-hoc approaches all describe methodologies or styles for the software development lifecycle. The Waterfall model is a sequential design process. An Iterative process involves cycles of development to build a system piece by piece. Ad-hoc development, while unstructured, is still a way of approaching software creation (often called "code and fix").

In contrast, the term "Big Bang" most commonly and distinctly refers to a system implementation or adoption strategy, not a development model. This strategy involves deploying the new system all at once, replacing the old system in a single event. While a very simple, high-risk "Big Bang" development model exists, its primary definition in business and systems analysis relates to deployment, making it the exception in a list of development approaches.

A. Iterative Process: This is a major category of modern SDLC models, including Agile and Spiral, where development is done in repeated cycles.

B. Ad-hoc Development: This describes an unstructured approach to software development without a formal methodology. It is still a (chaotic) way of approaching the development process.

C. Waterfall: This is the classic, foundational SDLC model, characterized by a linear and sequential progression through distinct phases.

1. For Waterfall and Iterative Models:

Sommerville, I. (2011). Software Engineering (9th ed.). Pearson. In Chapter 2, "Software Processes," Sommerville describes "plan-driven processes" like the Waterfall model (Section 2.1.1) and "iterative development" as a fundamental part of incremental and spiral models (Section 2.1.3).

2. For Big Bang as an Implementation/Adoption Strategy:

Saaksvuori, A., & Immonen, A. (2008). Product Lifecycle Management. Springer. In Chapter 10, "PLM Implementation," the authors discuss implementation strategies, stating, "The main strategies are the big bang, the step-by-step (or incremental) approach and the parallel running of the old and new systems" (p. 201). This clearly defines "Big Bang" as a deployment/implementation method, distinct from an SDLC model.

Kloppenborg, T. J. (2019). Contemporary Project Management (4th ed.). Cengage Learning. Chapter 13 discusses project closure and implementation, contrasting a "Big Bang" (or direct cutover) approach with phased and parallel implementation approaches. This source is used in university project management courses.

3. For Ad-hoc as a Development Approach:

Pressman, R. S., & Maxim, B. R. (2015). Software Engineering: A Practitioner's Approach (8th ed.). McGraw-Hill. The book often contrasts structured engineering processes with earlier, less formal "code-and-fix" or ad-hoc methods, establishing it as a baseline development approach from which formal models evolved.