Abstract. The error-prone process of formal specification and verification of large systems requires an efficient, evolutionary formal development approach. Development graphs have been designed to support such an approach. They can formally represent the actual state of a software development comprising specification and verification work in a structured way and assist the user in her evolutionary development by the incorporated change management support. In this paper we extend this work with respect to heterogeneous development graphs allowing one to make use of different institutions, i.e. logics, for specifying and verifying large developments. We also push forward the idea of stringent locality of definitions by introducing pre-signatures and pre-signature morphisms, which allow us to build up signatures in an incremental and parametric way.