The ongoing digital transformation in industry applies to all product life cycle's stages. The design decisions and dimensioning carried out in the early conceptual design stages determine a huge part of the product's life cycle costs (LCC). The automation of the conceptual design phase promises therefore huge gains in terms of LCC. Design grammars encode design processes in production systems made up of rule sequences which automatically create an abstract central product model (central data model) from given requirements. Graph-based design languages use the Unified-Modeling-Language (UML) to define the product entities (classes) supporting object-oriented inheritance. Graphical rules instantiate the classes and iteratively assemble the central model. This paper proposes to extend the design languages by introducing methods (operations). This allows the use of object-oriented design patterns and interface mechanisms as object-oriented principles are then fully implemented. A graphical mechanism to model the method calls is presented which integrates seamlessly into the graph-based design language's graphical rule specification. The object oriented design grammar enables modularization and reusability of engineering knowledge. The integration of engineering domains is enhanced and multistakeholder collaboration with access control (information security) becomes feasible.