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A requirement specifi es fl ows or
conditions that have to be met by the system.
228 CHAPTER 4 SysML??”The Systems Modeling Language
A requirement is a stereotyped class. This means that a requirement has the
semantics of a class, extended by the specifi c semantics and properties of the stereotype,
which will be discussed below.
Two elementary properties of a requirement are a unique identifi er (ID) and a
descriptive text. They are attributes of the stereotype, which means that they can
be described for any modeled requirement.
The ID is a simple string. It is up to the tool or to the modeler to ensure that it
is unique. SysML does not dictate a structure for the ID.
The explanatory text is also a simple string. It includes a description of the
requirement itself or references an external source, for example, a legal code or
a data record in a requirement management tool. In the latter case, the original
requirements is stored externally, while the SysML requirement is merely a reference
in the model to produce the connection to design and test elements.


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