SysML Requirements

SysML Requirements⌘

A Requirement⌘

• A requirement specifies a capability or condition that must (or should) be satisfied.
• A requirement may specify a function that a system must perform or a performance condition a system must achieve.
• SysML provides modeling constructs to represent text-based requirements and relate them to other modeling elements.
• The requirements diagram can depict the requirements in graphical, tabular, or tree structure format.
• A requirement can also appear on other diagrams to show its relationship to other modeling elements.

Requirements Tabular Representation⌘

Requirements relationships⌘

• Several requirements relationships are specified that enable the modeler to relate requirements to other requirements as well as to other model elements.
• These include relationships for defining a requirements hierarchy, deriving requirements, satisfying requirements, verifying requirements, and refining requirements.

requirement containment⌘

• A composite requirement can contain subrequirements in terms of a requirements hierarchy, specified using the UML namespace containment mechanism.
• This relationship enables a complex requirement to be decomposed into its containing child requirements.

requirement containment example⌘

A Package Containing Requirements⌘

copy⌘

• A Copy relationship is a dependency between a supplier requirement and a client requirement that specifies that the text of the client requirement is a read-only copy of the text of the supplier requirement.

copy example⌘

deriveReqt⌘

• A DeriveReqt relationship is a dependency between two requirements in which a client requirement can be derived from the supplier requirement.
• For example, a system requirement may be derived from a business need, or lower-level requirements may be derived from a system requirement.
• The arrow direction points from the derived (client) requirement to the (supplier) requirement from which it is derived.

deriveReqt example⌘

deriveReqt & problem example⌘

satisfy⌘

• A Satisfy relationship is a dependency between a requirement and a model element that fulfills the requirement.
• The arrow direction points from the satisfying (client) model element to the (supplier) requirement that is satisfied.

verify⌘

• A Verify relationship is a dependency between a requirement and a test case or other model element that can determine whether a system fulfills the requirement.
• The arrow direction points from the (client) element to the (supplier) requirement.

refine⌘

• The refine requirement relationship can be used to describe how a model element or set of elements can be used to further refine a requirement.
• For example, a use case or activity diagram may be used to refine a text-based functional requirement.

Example⌘

trace⌘

• A generic trace requirement relationship provides a general-purpose relationship between a requirement and any other model element.
• The semantics of trace include no real constraints and therefore are quite weak.
• It is recommended that the trace relationship not be used in conjunction with the other requirements relationships.

Requirement relationships as matrices⌘

Non-normative Requirements subclasses⌘

• Annex E: Non-normative Extensions of the SysML specification describes an example of a non-normative extension for a requirements profile.
• More specialized requirement stereotypes are introduced: functional, interface, performance, physical, design constraint.
• Additional properties are proposed: source, risk, and verifyMethod