If a role is typed by a classifier other than Class, the name compartment of the part box symbol contains the appropriate keyword (e.g., «component») above the name. Source Unified Modeling Language 2.5.1
The «Subsystem» stereotype for UML Components has nothing to do with the non-normative SysML «subsystem» stereotype for Blocks
GOTCHA: UML Component «subsystem» vs non-normative SysML «subsystem» Gallery Tutorial TRAIL: Webel's ultimate guide to Systems Modeling Language (v1) with MagicDraw/Cameo Section 14:01: UseCases in SysML Slide kind hybrid diagram UML Profile Diagram
A subject of a UseCase could be a system or any other element that may have behavior, such as a Component or Class. Source Unified Modeling Language 2.5.1
