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Software Development Life Cycle Models

What is a Software Development Life Cycle (SDLC)?

Before we talk about Software Development Life Cycle Models, we first need to understand what a Software Development Life Cycle (SDLC) is.

A Software Development Life Cycle, also called SDLC, is a process for developing software following systematic and clear procedures. It covers the stages that an idea must go through from an idea until it becomes an actual product.

It generally consists of 5 stages starting from Analysis to Design then Creation to Testing and finally Deploying the software.

The Software Development Life Cycle can be further broken down into 7 common phases that most systematic and planned software development goes through.

The phases are introduced below. 

7 Phases of the Software Development Life Cycle (SDLC)

Planning

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The planning phase is when the software’s requirements and purpose are defined.

During the planning phase, the objectives, labor, time, and other resources are clearly set out as a guideline for future operations.

Requirement Analysis

User needs, market research, technical requirements, etc. are analyzed to determine what exactly the software will do and what the software requires (resources).

Design 

During design, the architecture, user interface, security, etc. will be decided upon. It’s the last phase before actual development.  

Development

After product design, the development team(s) can begin the actual coding of the software/system. The development phase is usually the longest in the SDLC.

Testing

After product or iteration development, the whole software is tested for bugs, functionality, and performance. The testing phase continues until all the identified issues are resolved or feature acceptance criteria are met.

Deployment

After testing, the final software is released to users.

Maintenance & Operations

After the product is deployed, certain post-development activities take place. 

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Examples include:

  • Error/Bug Correction
  • Updates & Upgrades to suit changing systems and requirements
  • Enhancements

What are Software Development Life Cycle (SDLC) Models?

SDLC Models also called Software Development Process Models are unique approaches to developing software based on the SDLC. Each SDLC model has a different configuration or arrangement of SDLC phases to produce the best product.

Some models or methodologies follow a sequential phase arrangement whereas others adopt a more repetitive phase arrangement. Others can even be combinations of several phase arrangement principles. 

Regardless of the SDLC model type, each model aims to efficiently deliver a finished product that works correctly.

Below are 5 popular SDLC Models. 

5 Types of Software Development Life Cycle Models – SDLC Models and Methodologies

Software Development Life Cycle ModelWaterfall

The Waterfall model follows a straightforward and sequential transition between development phases. This means, when using a Waterfall model or methodology, you can only move on to the next phase of development after you complete the previous one. You cannot work on 2 or more development phases at the same time.  

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The Waterfall methodology is one of the oldest and easiest project management models available.

The Waterfall model is ideal for development projects where the requirements are fixed and well documented. The Waterfall model can also be used in the following situations:

  • Project requirements and expected outcomes are clear for the the stakeholders
  • The Product Definition is fixed and stable
  • The technology and tools needed are static and not dynamic
  • The requirements are precisely and clearly described

Advantages

  • Simple and easy to follow
  • The stages and work needed are clearly defined so it’s easier to plan ahead
  • Ideal for fixed requirement projects 
  • The process and output is well documented

Disadvantages 

  • Product is only available near the end of the SDLC
  • Bad for complex and Object-oriented projects
  • Bad for ongoing projects that require long maintenance and updates
  • Unsuitable for projects whose requirements might change
  • Unsuitable for software for a volatile market 

Software Development Life Cycle ModelSpiral

The Spiral model is an approach that combines the systematic Waterfall model and the repetitive Iterative model into one complex software development life cycle model. A spiral model has 4 phases which are repeated again and again in iterations called Spirals. 

The four phases are:

  1. Planning
  2. Design
  3. Construction
  4. Evaluation

The Spiral Model is best for projects where:

  • The customer is unsure of the project’s requirements
  • Edits or revisions are needed during the project’s development life cycle
  • You need an early prototype to gather client feedback 

Advantages

  • Easy to adjust the product to changing requirements
  • Software is produced early in the development life cycle
  • Best for large and complicated projects
  • Better risk management due to early functional product

Disadvantages

  • Complex to understand and follow
  • Hard to manage the time needed to complete the project
  • Unsuitable for small projects as it’s expensive to implement
  • The spiral might on indefinitely

Software Development Life Cycle ModelV-Shaped

The V-Shaped model is a modified version of the Waterfall model. The key difference being that, the V-shaped has earlier testing phases than the Standard Waterfall model.

However, the V-shaped model still follows a sequential transition between phases as the next phase can only begin after the current one ends. 

The V-shaped model can be used when:

  • The project is short
  • The Product Definition is fixed and stable
  • The technology and tools needed are static and not dynamic
  • Projects that need accurate product testing
  • The requirements are precisely and clearly described

A V-shaped model shares many of the same advantages as the Waterfall model.

Advantages

  • Works best for small and fixed requirement projects.
  • Easy to understand and use
  • Easy to manage and review

Disadvantages

  • Unsuitable for long and complex projects
  • Hard to return to a phase and alter functionality
  • Working software produced late in the SDLC
  • Inflexible to adjust during development
  • Unsuitable for projects with changing requirements

Software Development Life Cycle ModelIterative

An Iterative model aims to overcome the shortcomings of the Waterfall model by building a functioning system early in the SDLC. The software is built by repetitively adding small working increments until we have a complete product.

An Iterative model consists of repeated “mini-waterfalls” with each waterfall delivering a functional output called an increment to the product.

Advantages

  • Easy to discover errors or flaws early in the SDLC
  • A working model is produced early in the SDLC for assessment and feedback
  • Works best for large and complex projects
  • Project progress is measurable
  • Easy to adjust to changing requirements
  • Parallel Development is possible.

Disadvantages

  • Unsuitable for smaller projects
  • Complex to manage
  • More resource-intensive due to repetition

Software Development Life Cycle ModelsAgile

An Agile model is an approach that combines iterative and incremental processes in one development methodology. In the Agile model, a project is broken down into smaller builds that can be cumulatively added onto each other until project completion. 

Each completed development iteration, called a sprint, results in a new product build. Each sprint or iteration is also time-bound.

The principle behind Agile is to repetitively deliver small working chunks of a product instead of trying to deliver everything at once.

The Agile model includes a lot of development methods like Scrum, Feature-Drive Development, Extreme Programming, Crystal Clear, etc. These and many others are referred to as Agile methods.

Advantages 

  • Promotes teamwork and collaboration between different teams
  • A partial working product is delivered early in the SDLC
  • Best for projects with changing requirements
  • Does not require a lot of resources
  • High-level understanding between project owner and developers
  • Suitable for most projects

Disadvantages 

  • Unsuitable for projects with complex dependencies
  • Needs specialized personnel to implement
  • Relies heavily on customers and owner direction, so if they are wrong or vague, the project may fail.
  • Needs a highly professional and adapted team to work well

Conclusion – The Best Software Development Life Cycle Model?

No SDLC model can be called the best. Each Software Development Life Cycle Model (SDLC Model) has a scenario where it gives the best results when applied.

SDLC Models are like shoes. A formal shoe is best for suit and tie events. A pair of sneakers can be your daily driver. A safety shoe is best for risky and slippery environments. However, it is up to you to identify your environment before you choose your shoe.

Similarly, it is your responsibility to identify your project’s needs and requirements before you choose the right Software Development Life Cycle Model for it.

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