Different models of the software development life cycle (SDLC)

Before we talk about the models of the software development life cycle, it is good to briefly review some of the items. As we said in the SDLC article, the software development lifecycle is a standard approach to managing the various phases of a software project. This method has different stages, which the output of each is assumed to be the input of the next one. Planning and analysis, defining requirements, prototype design, software testing, deployment, and maintenance are the different stages of general SDLC.

Different SDLC Models

However, the general life cycle model can not be used in all conditions due to some practical problems ahead:

  • A simple system may have one planning phase, while a more complex one may require more than two definition stages.
  • With prototypes’ help, a large part of system development may take place during the system definition phase.
  • In the general model, testing and integration occur after coding, but you may implement and test elements daily in some software projects. In such cases, testing, integration, and accreditation are actually combined with the project coding.
  • With the spread of the Third Industrial Revolution, namely 3D printing and digital production, initial development and even initial production may occur during the concept development phase.
  • As its name implies, the software is a soft and flexible tool that facilitates analysis, design, implementation, testing, and iterative delivery (we can execute and test our code immediately and re-implement it if necessary). Compare this with the system of entirely physical elements that you cannot build and retest quickly and easily!
  • You can buy, sell, deliver, and upgrade software anywhere in the world connected to digital communications; therefore, its logistics and support are very different and more cost-effective than hardware.

Given the above, we find that there must be many models of the software development life cycle for different systems. In the following, we review eight standard SDLS models.



Waterfall model of software development life cycle

Although the waterfall approach is one of the oldest life cycle models, its popularity has declined in recent years. Waterfall has a rigid structure that requires project managers to define all software project requirements at first. After performing this first step, permission to enter the design and development stages is issued. As the waterfall’s name indicates, it is impossible to go back, and each phase starts after the end of the previous one.

When the development is complete, the programmers test the software according to the basic requirements and assign the corresponding tasks.

Software companies need more flexibility than what this SDLC model offers. However, the waterfall life cycle method is still a powerful solution for software projects, especially in agreements with government contractors.


The sequential steps in the waterfall life cycle model are:

  • Requirements: At this stage, the team defines all software production requirements and records them in the requirements specification document.
  • System design: At this stage, the professionals study the complete specifications of the first stage requirements. Based on these investigations, they design the system and identify hardware and software needs to determine the system’s overall architecture accordingly.
  • Implementation: At this stage, using system design inputs, programmers build small-scale programs called units. The units are merged in the next step and tested to evaluate performance. This stage is also called the unit testing stage.
  • Verification: Specialists test all units that have been integrated into a system during production and implementation. After integration, they test the whole system again to eliminate defects.
  • Maintenance: Some problems occur only in the customer environment. Programmers make changes and sometimes provide a new version to upgrade the system to solve these difficulties. They reinstall changes or a new version in the customer’s environment.

Iterative model

This method uses the cascade model and its cycle several times in small increments. Instead of putting the whole project in life cycle phases, each phase turns into several mini-projects that add value as the product progresses.

The iterative approach covers many of the Agile model goals, except that in this SDLC model, customers are less involved and the range of each step increment is typically constant.

This model is often useful in he following scenarios:

  • We have defined and identified the requirements of the whole system.
  • We have defined major requirements and new functions or new software upgrades.
  • Where we have limited time.
  • The team must use new technologies during implementation.
  • The team does not have enough human resources to carry out the whole project and must recruit at every stage.
  • Some features or goals of a project are risky and may change later.

DevOps model

DevOps is one of the newest life cycle models recently used by various software and IT companies. As the name implies, its purpose is to bring together the development team and the operations team to simplify and streamline delivery and support.

DevOps method makes changes smoother and reduces organizational risk. This is one of the advantages of this model. Teams must have flexible manpower to achieve a duplicate arrangement.


V-Model of software development life cycle

It is a kind of upgraded waterfall model. The V-Model stages change upward after the implementation (coding) step. Like the waterfall, this SDLC model is rigorous; the next phase starts when the previous step gets completed.

Due to the inflexibility mentioned above and high risk, this life cycle model is not suitable for small projects. However, as V-model is easier to manage and control, it is the right choice for projects where the requirements are fixed, completely transparent, and where initial testing is necessary.


Spiral model

This model allows teams to apply several life cycle models according to their risk pattern. Like a combination of cascading and repetitive models, Spiral has the challenge of when to move on to the next phase.

Businesses that are unsure of their requirements or expect major changes during risky projects can take advantage of this scalability.


Lean model

The lean and agile models are so close that both emphasize fast delivery and continuous evolution. Nevertheless, the lean life cycle model is rooted in manufacturing and production practices, so that extra and useless work is the most significant risk for the organization.

In the case of software projects, the focus of the lean model is on reducing the waste of time, cost, and range in each phase. This approach is essential for organizations with strict hardware requirements and other strict contracting requirements.


Agile model of software development life cycle

The agile method is in stark contrast to the waterfall method. Instead of extracting requirements, designing and testing them in large sequential steps, the agile SDLC model brings them all together in ongoing processes that require the presence of developers, management, and customers.

The work is broken down into 2 to 4-week intervals, and the teams are responsible for meeting the customers’ basic needs and testing over time. The agile approach is suitable for small organizations, especially startups, where speed and flexibility are essential.


Prototyping model

In the prototyping life cycle model, the design team focuses on producing a new system, software, or application prototype. This sample does not have a thoroughly tested performance and is only for the customer to understand what will come to market. After this step, the team collects feedback and applies it throughout the life cycle.

This method is beneficial for companies working in emerging industries and new technologies.


Choosing the best life cycle model

Before choosing the best model for your company or organization, it is better to memorize that one solution does not necessarily work for all organizations or scenarios. For some projects, the waterfall method may work, while for others, the iterative, agile, or repetitive approach is practical.

As you see, various organizational factors can influence on choosing life cycle models for a particular system. Technical aspects can also affect the type of life cycle models suitable for a given scenario. For example, system requirements (depending on the development’s framework and nature) may be predetermined or may change.

All of these considerations lead to the selection of different life cycle models.

The life cycle model chosen can affect system design and development. There are some incremental and evolutionary models in addition to the traditional, predetermined, sequential, and single-pass development process. However, we should emphasize that there is no one-size-fits-all approach.

Incremental and evolutionary approaches History

Incremental and evolutionary approaches have been used since the 1960s. In these approaches, the project provides an initial capability and reaches the desired system in subsequent deliverables. This method is precious in the following cases:

  • Rapid research and implementation of part of the system is required.
  • Requirements are not clear from the beginning or change rapidly.
  • Budget is limited
  • The customer wants to keep the system open to new technologies.
  • Experiments are necessary to develop successive versions.

For example, about the iterative life cycle model, each of the iteration cycles incorporates system elements from the previous iteration and adds new capabilities to the evolving product. (Like software that is partially coded each time, developers add new features to the old code). Iterative development has advantages that include:

  • Ongoing integration, validation, and accreditation
  • Evolving product;
  • Frequent shows and presentations of progress;
  • Early detection of defects;
  • Early warning of process problems;
  • Systematic integration of unavoidable rework;

SOJECT and Different models of the software development life cycle (SDLC)

SOJECT is one of the successful companies in the field of software production. Our specialists work in various areas to produce and develop customers’ software.

Planning software development stages, based on the software life cycle models, is one of the steps done in SOJECT to provide a high-quality final product that is appropriate for the customer.

For more information, you can contact us through our site.

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