Wednesday, September 13, 2006

Feature Driven Development (FDD)

Overview

FDD is a model-driven short-iteration process that consists of five basic activities. For accurate state reporting and keeping track of the software development project milestones that mark the progress made on each feature are defined.

Activities

FDD describes five basic activities that are performed within the software development process. In the figure on the right the meta-process model for these activities is displayed. During the first three sequential activities an overall model shape is established. The final two activities are iterative for each feature.


Develop Overall Model

The project starts with a high-level walk through of the scope of the system and its context is performed. Next, detailed domain walkthroughs are held for each modeling area. In support of each domain, walkthrough models are then composed by small groups which are presented for peer review and discussion. One of the proposed models or a merge of them is selected which becomes the model for that particular domain area. Domain area models are merged into an overall model, the overall model shape being adjusted along the way.

Build Feature List

The knowledge that is gathered during the initial modeling is used to identify a list of features. This is done by functionally decomposing the domain into subject areas. Subject areas each contain business activities, the steps within each business activity form the categorized feature list. Features in this respect are small pieces of client-valued functions expressed in the form , for example: 'Calculate the total of a sale' or 'Validate the password of a user'. Features should not take more than two weeks to complete, else they should be broken down into smaller pieces.

Plan By Feature

Now that the feature list is complete, the next step is to produce the development plan. Class ownership is done by ordering and assigning features (or feature sets) as classes to chief programmers.

Design By Feature

A design package is produced for each feature. A chief programmer selects a small group of features that are to be developed within two weeks. Together with the corresponding class owners, the chief programmer works out detailed sequence of diagrams for each feature and refines the overall model. Next, the class and method prologues are written and finally a design inspection is held.

Build By Feature

After a successful design inspection a per feature activity to produce a completed client-valued function (feature) is being produced. The class owners develop the actual code for their classes. After a unit test and a successful code inspection, the completed feature is promoted to the main build.

Milestone

Since features are small, completing a feature is a relatively small task. For accurate state reporting and keeping track of the software development project it is however important to mark the progress made on each feature. FDD therefore defines six milestones per feature that are to be completed sequentially. The first three milestones are completed during the Design By Feature activity, the last three are completed during the Build By Feature activity. To help with tracking progress, a percentage complete is assigned to each milestone. A feature that is still being coded is 44% complete (Domain Walkthrough 1%, Design 40% and Design Inspection 3% = 44%).

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