The spiral model of software development life cycle includes the idea of iterative development of the prototype model with a systematic controlled approach of the waterfall model. This SDLC model is similar to the SDLC incremental model with high emphasis placed on risk analysis phase. The spiral modeling approach is ideal for developing software projects that is revealed in various versions. The behavior of this model allows for incremental releases of the product, or incremental refinement through all iterations around the spiral.
When a software application project develops under this SDLC spiral model the project reputedly passes through these phases in iterations. These iterations are called spirals of the model. The baseline of the spiral model, starting from the planning phase, than the objective identification and constraints iteration under works, after object identification phase the model transfer the control to the risk analysis and evaluate and at last the testing and execution iteration of spiral model is working on. When these all iterations are completed and the product require more functional enhancement then this cycle of spiral model is compile continuously until the customer desired task being completed.
Design phases | Advantages | Disadvantages | Pros & Cons | Applications
To elaborate the working of SDLC spiral model consider an example of spiral model. Let Microsoft window operating system from Window 3.1 to Window 2003. We may prefer to Microsoft windows 3.1 Operating System as the first iteration in the spiral approach. The product was released and evaluated by the customers, which include the market large. After getting the feedback from customers about the windows 3.1, Microsoft planned to develop a new version of windows operating system. Windows’95 was released with the functional enhancement and graphical flexibility. Similarly, other versions of windows operating system were released these all are the result of applying spiral model all iteration.
Design phase of SDLC Spiral model:
In the spiral modelling approach each iteration follows the phase-wise linear approach in the software development process. At the end of successive iteration, the customer evaluates the software and reviews the product and provides positive and/or negative feedback as per the required functionality of the software product. Software development expertise team members review the feedback and based on the feedback reviewing take action on the product and re-enter to the process into the next iteration and subsequently. The process of iteration continues throughout the life of the software.
The spiral model has four standard phases, listed as;
Planning and Analysis
Risk analysis and evaluation
Objective identification and constraints
Testing and execution (Design)
Following phases in the figure below representing the different phases of SDLC spiral model:
- Planning phase:
In the planning phase the system requirements are identified and gathered. This phase of spiral modeling is also called system identification phase. In the spiral model the iteration process is start with gathering the business requirements in the baseline spiral. In the subsequent spirals as the product matures, identification of system requirements, subsystem requirements and unit requirements are all done in this phase.
This identification and/or planning phase also includes understanding the system requirements by continuous communication between the customer and the system analyst team members. Requirements like Business Requirement Specifications (BRS) and System Requirement specifications (SRS). At the end of the spiral the product is deployed in the identified market.
- Evaluation and Risk Analysis:
Risk Analysis phase includes identification, estimation and monitoring of technical feasibility of developed system and management risks, such as schedule slippage and cost overrun. After testing the build, at the end of first iteration, the customer evaluates the software and provides feedback.
In this phase also includes of risk analysis a process is undertaken to identify risk in the product and to handle that risk development team have alternate solutions. At the end of this phase a prototype is produced that works as an alternate solutions are suggested and implemented if an unwanted risk found during the risk analysis phase.
- Construct or Build:
This phase refers to the actual production of the software product at every spiral or iteration process. This phase of spiral model have software development along with testing of product before launching. In the baseline spiral when the product is just thought of and the design is being developed a POC (Proof of Concept) is developed in construct or build phase by the designed expertise to get customer feedback.
Then in the subsequent spirals or iteration with higher clarity on requirements and design details a working model of the software called build is produced with different version number of system product. These builds are sent to customer for feedback. This phase of spiral model is also called engineering phase.
- Design:
Design phase is also known as evaluation phase of SDLC spiral model. This phase starts with the conceptual design in the baseline spiral and involves architectural design, logical design of modules, physical product design and final design in the subsequent spirals. The main agenda of this phase is to allow the customer to evaluate the output of the project to data before the project continues to the next spiral.
These four phase of spiral model cover in a single iteration process. For the next iteration the customer evaluation, software development process are enters and subsequently follows the linear approach to implement the feedback suggested by the customer. The process of iterations along with the spiral model continues throughout the life of developed software.
Advantages and disadvantages of SDLC spiral model:
Every software development model has own advantages and disadvantages that decide the working area of the model. Here we are listing all the advantage and disadvantages of spiral model:
Advantages of Spiral model:
The advantage of spiral lifecycle model includes the high amount of risk analysis that supports avoidance of system risk. In addition this model allows for elements of the product to be added in when they become available or known. This assures that there is no conflict with previous requirements and design. Spiral modelling approach is good for large and mission-critical projects.
This modelling approach is consistent with those product developments that have multiple software builds and releases and allows for making an orderly transition to a maintenance activity. Another positive aspect of this spiral modelling approach is that this model forces early user involvement in the system development effort.
Disadvantages of Spiral model:
In the disadvantages of spiral model includes, it takes very strict management to complete such products and there is a risk of running the spiral in indefinite loop. So the discipline of change and the extent of taking change requests are very important to develop and deploy the product successfully. The success of developed system depends on the risk analysis phase completely. This modelling approach is not flexible for the smaller projects.
Pros and Cons of SDLC Spiral model:
There are many pros and cons of spiral model. In the following list we are trying to cover all pros and cons of SDLC spiral model, follow us;
| Prose of spiral model | Cons of spiral model |
| Changing requirements can be accommodated. | Management is more complex. |
| Allows for extensive use of prototypes | End of project may not be known early. |
| Requirements can be captured more accurately. | Not suitable for small or low risk projects and could be expensive for small projects. |
| Users see the system early. | Process is complex |
| Development can be divided into smaller parts and more risky parts can be developed earlier which helps better risk management. | Spiral may go indefinitely. |
| Large number of intermediate stages requires excessive documentation. |
Application of SDLC spiral model:
Various software application development models available in market those are used by the software industries. Each software development application has different requirements based on internal and external factors. Similar for the spiral model, this modeling approach is very widely used in the software industry as it is in synch with the natural development process of any product i.e. learning with maturity and also involves minimum risk for the customer as well as the development firms. Following are the typical uses of Spiral model:
- Requirements are complex and need evaluation to get clarity.
- New product line which should be released in phases to get enough customer feedback.
- When costs there are a budget constraint and risk evaluation is important.
- Long-term project commitment because of potential changes to economic priorities as the requirements change with time.
- For medium to high-risk projects development.
- Customer is not sure of their requirements which are usually the case.
- Significant changes are expected in the product during the development cycle.
