In aspect-oriented modeling (AOM), a design is de- scribed using a set of design views. It is sometimes neces- sary to compose the views to obtain an integrated view that can be analyzed by tools. Analysis can uncover conflicts and interactions that give rise to undesirable emergent be- havior. Design models tend to have complex structures and thus manual model composition can be arduous and error- prone. Tools that automate significant parts of model com- position are needed if AOM is to gain industrial acceptance. One way of providing automated support for compos- ing models written in a particular language is to define model composition behavior in the metamodel defining the language. In this paper we show how this can be done by extending the UML metamodel with behavior describ- ing symmetric, signature-based composition of UML model elements. We also describe an implementation of the meta- model that supports systematic composition of UML class models.