Requirements languages are often defined as metamodels for the standardization of a system’s requirements specification. The unification of these metamodels benefits general analysis and interoperability between requirements models. Even tough many authors already discuss systematic composition approaches, this application for requirements languages’ metamodels is still little explored. Therefore, we create a unified metamodel for User Story and UML diagrams relying on non-domain-specific composition frameworks by assessing common points in related work. The resulting model was used to discuss the applicability of these methods on requirements domain.