Requirements realizations represent how one or more requirements are fulfilled in the design. This can take
various forms. It may include, for example, a textual description (a document), class diagrams of participating classes
and subsystems, and interaction diagrams (communication and sequence diagrams) that illustrate the flow of interactions
between class and subsystem instances.
In a model, requirements realization is typically represented as a UML collaboration that groups the diagrams and other
information (such as textual descriptions) that form part of the realization. If using use cases, the
collaboration may be further stereotyped as a use-case realization.
Note that there can be more than one realization of the same set of requirements. This is particularly important
for larger projects, or families of systems where the same requirements may be designed differently in different
products within the product family. Consider the case of a family of telephone switches which have many requirements in
common, but which design and implement them differently according to product positioning, performance and price.