Which design object is concerned with external system interactions required by the application?

The design object that focuses on external system interactions required by the application is Integration. In the context of Appian, integrations are crucial for enabling communication between the Appian application and other external systems, such as databases, third-party services, or APIs.

Integrations allow the application to fetch data, send data, or perform operations in real-time by connecting to these external entities. This capability is essential for creating a seamless user experience and for ensuring that your application can utilize external resources effectively. For instance, an integration might be used to pull customer details from a customer relationship management (CRM) system or to send order information to an enterprise resource planning (ERP) system.

In contrast, the other options address different aspects of the application design. Sites are related to the overall visual organization and user experience, interfaces pertain to how users interact with the application, and release plans deal with project management and deployment timelines. Therefore, while all these design objects are important, only integrations specifically cater to the interactions with external systems.