Cross-Cutting Constructs
Organization, views, allocation, and extension
Packages organize the model. Distinguish namespace containment (ownership) from import (public or private), which only makes names visible. A «model» is a kind of package serving as a model root.
Views and viewpoints structure how stakeholders see the model. A viewpoint names the stakeholders and their concerns; a «view» conforms to a viewpoint («conform») and exposes a subset of the model; a diagram is only a rendering of a view, not the view itself.
Allocation is the cross-cutting «allocate» dependency that maps elements across abstraction levels: behavior to structure (an action or activity allocated to a block), structure to structure (logical to physical), and requirements to design. It can appear on many diagram types, which is why it is treated as cross-cutting rather than as a diagram of its own.
SysML reuses a subset of UML diagrams and adds requirement and parametric diagrams; stereotypes and profiles extend the language, and value types carry units and dimensions so quantities are comparable.
Traps: calling a diagram a view; assuming a viewpoint contains model elements; confusing «conform» with «trace»; thinking allocation only maps structure; forgetting that applying a stereotype is a dependency to the profile that defines it.
Rule of thumb: if a relationship cuts across abstraction levels or diagram kinds without implying ownership, it is allocation or traceability - not containment.