Software spiral model

Software spiral model is an evolutionary software process
 model which is a combination of an iterative nature of prototyping and systematic aspects of traditional waterfall model.

History

´  Defined by Barry Boehm in his 1988 article.

´  It was not the first model to discuss iterative development, but it was the first model to discuss why the iteration matters.

When to use spiral model:

When cost and risk evaluation is important.

For medium to high risk projects.

Users are unsure of their needs.
Requirements are complex.
Significant changes are required.

Phases

It has four phases:

´  Planning

´  Risk Analysis

´  Engineering

´  Evaluation

Planning

´  It includes cost ,schedule and resources for the iteration.

´  It also involves understanding the system requirements.

´  Allows communication between the system analyst and the user.

Risk Analysis

´  All possible alternatives which can help us developing and cost effective project are analyzed.

´  The phase itself identify and resolve  all type of risks.

´  Identification of potential risks.

Engineering Aspects

´  The actual development of the project carries out.

´  The output of the phase is passed out through all the phased iteratively in order to obtain improvements.

Evaluation

´  Customer Feedback.

´  Monitoring Risks.

Customer Evaluation

´  Developed product is passed towards the customer to get their feedback and suggestions.

´  This phase is very similar to the testing phase.

Applications

´  Used for large projects.

´  For smaller projects, the concept of agile development process becomes viable alternative.

´  Reasonable to use in the software where the business goals are unstable.

Advantages

´  Changing requirements can be accomodated.

´  Allows extensive use of prototypes.

´  Requirements can be captured more accurately.

´  User can get to see the system early.

´  Early and frequent feedback from the users.

´  Additional functionality or changes can be done at early stage.

´  Cost estimation becomes easy as the prototype building is done in small fragments.

´  Continuous or repeated development helps in risk management.

Disadvantages

´  Risk of not meeting the schedule or budget.

´  Not suitable for small and low risk projects could be expensive for small projects.

´  Process is complex.

´  Operation needs to be managed strictly.

´  Risk assessment expertise is required

´  Documentation is more as it has intermediate phases.