Instead of UML diagrams, an alternative approach is using graph grammars according to G. Rozenberg (1997) to specify meta-models. With the capability of formally specifying syntax in a visual fashion, graph grammars have gained much attention in recent years. Based on graph grammar formalism, called the reserved graph grammar (RGG) as stated in D.Q. Zhang et al. (2001), this paper proposes an intuitive yet formal approach to specifying models. More specially, given a graph grammar defining a meta-model, a visual language generator can automatically generate a graphical environment, which allows users to directly manipulate models by drawing box-line diagrams. A graph transformation engine underlying the environment can validate the integrity of user-designed models.