Abstract : The complex software development projects of today may require developers to use multiple requirements engineering approaches. Different teams may have to use different requirements modeling formalisms to express requirements related to their assigned parts of a given project. This situation poses difficulties in achieving interoperability and integration of requirements models for the purpose of reasoning on the overall system requirements. It is challenging to compose distributed models expressed in different notations and to reason on the composed models. In this paper we present a metamodeling approach which allows reasoning about requirements and their relations on the whole/composed models expressed in different requirements modeling approaches. In a previous work we expressed the structure of requirements documents as a requirements metamodel in which the most important elements are requirements relations and their types. The semantics of these elements is given in First Order Logic (FOL) and allows two activities: inferring new relations from the initial set of relations and checking consistency of relations. In this work we use the requirements metamodel as a core metamodel to be specialized for different requirements modeling approaches and notations such as Product-line and SysML. Mainly, the requirements relations in the metamodel are specialized to support relations in different requirements modeling approaches. The specialization allows using the same semantics and reasoning mechanism of the core metamodel for multiple requirements modeling approaches. To illustrate the approach we use an example from automotive domain expressed with two modeling approaches: product-line requirements models and SysML for system requirements.