A requirement specifies a capability or condition that must be satisfied. A requirement can define a function that a system must perform, or a performance condition a system must achieve. A requirement can appear in other diagrams to show its relationships to other model elements. Requirements have properties and links to other elements (requirements or model elements).
Modelio provides a spreadsheet editor dedicated to requirements analysis, as well as graphical support of requirements modeling.
In the example shown on the right, requirements are connected to model elements in order to express the model elements that refine, satisfy or verify them. The "DiscountTravelOrderingSite" component satisfies the "Internet booking access" requirement, because it implements functions related to the requirement. This requirement can be verified by running test cases related to the "Cancel Trip" and "Book Trip" use cases.
Requirement diagrams are based on the OMG’s SysML (System Modeling Language) standard.