7. What goes into the graph

A common first instinct is to put everything into the graph. Within a few sprints, the maintenance burden overwhelms the team. The methodology uses a rule, called the aperture, to decide what enters the graph. Every decision has a blast radius: the other decisions, artifacts and behaviours that have to change when the decision changes. A persona definition, a service boundary or a shared API contract has a wide blast radius, so it belongs in the graph. The wording on a single button affects nothing beyond that button, so it stays in the specification and the code. When the answer is unclear, the element stays out of the graph until the team is sure. The aperture starts narrow and widens as the team gains confidence, reaching its full width by about sprint twelve. The graph is partitioned by product, with one graph per product or application. Each graph is kept to one product, because the cost of a query grows with the size of the graph. Where two products integrate, links connect their graphs.

On the site: Aperture · The Blast Radius Test · How the Aperture Matures