White box

A white box is a view of a system or building block that shows its internal structure, in contrast to a black-box view, which shows only its interfaces and hides how it works inside. Opening the box reveals the smaller building blocks it’s composed of, and the internal and external relationships and interfaces between them.

A white-box view is typically the concern of a building block’s own building block view, one level down from wherever that block was previously treated as a black box. The same component can be a black box to one audience and a white box to another, depending on whether the reader needs to know how it’s built or only what it does.