1). The horizontal axis represents time, beginning
with the project concept at the left and ending with the product delivery on the right.
The vertical axis represents the level of integration, with the entire product at the
top, and the smallest meaningful units of software (classes and other types in C#)
at the bottom. A traditional project begins at the upper left with a product concept,
then works down the left side of the V, creating a specification that describes what
the product should do, and a design that describes how the product should be built
up from units. At the bottom of the V, developers code and test individual units.
Then the project works up the right side, integrating and testing larger collections
of units, until the complete product is delivered. (In projects with frequent releases,
there can be a V-diagram for each release.)
Overview 9
Unit testing
Component testing
System testing
Delivery
Code
Design
Speci?¬?cation
Concept
Rework
Rework
Re.
Figure 1.1. V-diagram showing traditional software project activities and schedule.
The V-diagram shows how each kind of testing activity (on the right side) is
supposed to check one kind of development product (at the same level on the left
side). This reveals the problem with traditional sequential development: the products
that are produced first (the specification and high-level system design) are tested last
(by tests on the integrated system, using scenarios suggested by customers or their
representatives among the developers).
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