CSC/ECE 517 Fall 2010/ch6 6c sg
Introduction
Agile software development is a conceptual framework for undertaking software engineering projects. Agile methods try to overcome the weakness found in Classic software development methodologies such as the waterfall model by using an iterative and incremental development approach. Most of the agile methods try to minimize the risk involved by developing the software in smaller time frames also known as iterations. Each iteration lasts for around one – four weeks. The characteristics of Agile manifesto published in 2001, by a bunch of software engineers can be summarized as follows: ( link)
Individuals and interactions over processes and tools Working software over comprehensive documentation Customer collaboration over contract negotiation Responding to change over following a plan.
Why do estimation
Planning is a very important aspect even for Agile projects. According to Stellman Greene , some say that estimation is a “Black Art”. What it means is that, the time required to finish a certain task varies from person to person. A certain individual might take a day to do a task that might only take a few hours of another’s time. Any estimate that is not close to the actual time required is a bad estimate. But a good formal estimation of cost and schedule improves the accuracy of the results and increases the likelihood of the project being delivered on time.
Traditional vs Agile approach
Layers in Agile Estimation
Thus, it helps in initial project planning. The 3 significant layers in Agile estimation and planning are
Release planning
Estimation of velocity is required and total feature size is expected. Usually to estimate the size of the products one needs to estimate the set of User stories that have been prioritized into next release. One needs to produce 2 estimates for each story, viz.
- The 50% estimate - This is the estimate in ideal days whereby the estimator feels confident that this estimate for completion of the story (design, develop, test, document) is equally likely to be under as over. This could also be thought as average estimate.
- The 90% estimate – This is the estimate in ideal days whereby the estimator feels 90% confident that the story will be completed (in other words that 90 times out of 100 thus story can be done in that ideal number of days). This is also known as the worst- case estimate.
Iteration planning
Here, estimation of velocity and size of each feature is performed. When the iteration is to be planned, the Product Manager and the Development leads can agree a theme for the iteration/sprint and can select the candidate stories from the estimated backlog that initially fit the available velocity of the team and that make the most sense to tackle together. Then in the iteration planning meeting these are presented to the team as a whole in order to get a next level down estimate. This involves the team breaking down the user stories into tasks and then estimating the tasks in ideal hours (for reference, and ideal day has 8 ideal hours).
Daily planning
Daily planning involves inspection of daily progress and planning for removing the obstacles faced in the process if any.