The selection of system use cases and scenarios is driven by the following:

• The benefit of the scenario to stakeholders: critical, important, useful.
• The architectural impact of the scenario: none, extends, modifies.
• The risks to be mitigated: performance, availability of a product, and suitability of a component.

In general the impact on architecture is correlated to the criticality. However, it must be noted that there might be critical use cases that have little or no impact, and vice versa, and some ancillary use cases can have a big impact on the architecture, which makes it questionable from a business perspective. The main concern is to select a set of use cases that ensures broad coverage (participation) of system internals, while still satisfying other constituencies.