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Containment Relationship

The Containment relationship's name well describes its purpose - it is used to show that one or more Requirements are contained in, or are grouped by, another higher-level Requirement. It is a fundamental and highly used relationship when modeling requirements for any system of even moderate complexity. A large system could have thousands, if not tens of thousands, of requirements, and these are best grouped together in hierarchies. An alternative to the use of the Containment relationship is to group Requirements using Packages. This method works when there are just two levels in the hierarchy or when you group Requirements by type - such as Stakeholder or Physical - but it has limitations when used more extensively.

The Containment relationship is available from relationships page of the SysML Requirements Toolbox.

This diagram shows the use of the Containment relationship to show two lower-level Requirements that are 'contained' by a higher-level Requirement.

The containment of Requirements can also be visualized in the Browser window, where containment is represented by elements being nested or, more formally, the contained elements are children of another Requirement. This leveling is possible for any elements in the repository, but has special meaning with Requirements. This image shows the same Requirements as in the previous diagram, but in the Browser window.

Note that nesting the Requirements in the Browser window does not create Containment relationships between Requirements. In fact, it is possible that the two different methods could be out-of-synch with each other because they are independent mechanisms.