Another relationship between requirements is <<refine>>. An example of requirement refinement is shown in Figure
Requirements have a number of derived attributes to store the status of the relationships reviewed in the above paragraphs. We will see later in this chapter that these attributes become particularly handy when requirement relationships are represented outside requirements diagrams.
Often requirements are elicited during the whole product life cycle and additional requirement diagrams are used to represent them. Hence the product requirements are typically laid out on a set of requirement diagrams.
SysML provides a generic model for requirements that allows the modeling of both functional and
requirement types are proposed in the appendix of the OMG SysML specification.4 Specific types of requirements (for example related to timing or scheduling) are handled by language extensions. SysML (like UML) supports a profile mechanism to extend the language. The Object Management Group (OMG) has released a series of modeling standards that address specific needs: for the modeling of
It should be noted that while SysML allows for requirements decomposition and allocation of requirements to design elements, MDSD does not encourage this. In general, MDSD promotes the derivation of requirements (as opposed to their allocation) through system decomposition and operations analysis.5
Additionally, much of the manual labor of creating requirements related diagrams can be automated, and should be, based on the artifacts resulting from following the MDSD process. For example, each use case or operation realization in a model represents the derivation of requirements on the participating collaborators. The functional requirements (operations) on each of the collaborators are derived from the use case or operation being realized.
4SysML 1.0 Specification
5See discussion in Chapter 2 concerning requirements decomposition and Cantor’s article on Functional Decomposition: Thoughts on Functional Decomposition, Rational Edge, June 2003, http://www.ibm.com/developerworks/rational/library/content/RationalEdge/apr03/Functiona lDecomposition_TheRationalEdge_Apr2003.pdf
