1. A computer-implemented method for merging a first modeled object with a second modeled object wherein the first and second modeled objects are modified versions of an initial modeled object, by merging a first graph and a second graph defining respectively the first and second modeled objects, wherein the method comprises: computing a first rewriting rule and a second rewriting rule, the first rewriting rule and the second rewriting rule corresponding respectively to a transformation of an initial graph into the first graph and the second graph, the initial graph defining the initial object, wherein the first rewriting rule specifies a first part from the initial graph which is to be replaced when transforming the initial graph into the first graph, a first replacement to replace the first part, a first interface between the first part and the first replacement, first morphisms from the first interface to the first part and to the first replacement respectively, and wherein the second rewriting rule specifies a second part from the initial graph which is to be replaced when transforming the initial graph into the second graph, a second replacement to replace the second part, a second interface between the second part and the second replacement, second morphisms from the second interface to the second part and to the second replacement respectively; determining a third rewriting rule by assembling the first rewriting rule and the second rewriting rule, wherein the third rewriting rule specifies an assembled part which is an assembly of the first part and the second part, an assembled replacement which is an assembly of the first replacement and the second replacement, an assembled interface which is an assembly of the first interface and the second interface, assembled morphisms from the assembled interface to the assembled part and the assembled replacement respectively; computing a merged graph by applying the third rewriting rule to the initial graph.