Which UML diagrams are structural?

Structural UML diagrams are designed to represent the static aspects of a system, showcasing how different components, entities, and relationships within a system interact and connect with one another.

Class diagrams fall under this category as they depict the classes, attributes, operations, and the relationships between classes in a system, fundamentally illustrating the blueprint of the system’s structure. Component diagrams, on the other hand, illustrate how components of a system (such as executables, libraries, and packages) are organized and how they communicate, providing a high-level overview of the system's architecture.

The other options consist of diagrams that describe the behavior and interactions within a system rather than its structure. Use Case and Sequence diagrams focus on the functional scenarios and the order of interactions, while Activity and State diagrams model the dynamic processes and states of a system. Deployment diagrams, while they show how software components are distributed across hardware, are different from structural diagrams as they lean more towards the physical deployment rather than the logical structure. Interaction diagrams also emphasize the flow of control and data among objects, again illustrating behavioral aspects rather than structural design.