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Diagrams (e.g., flowcharts, trees for hierarchical structures, or graphs for$nite state machines) are often needed as part of visual language systems and advanced user integaces, and are frequently application specijic. The implementation of editors for diagrams should be supported by a tool and based on a formal model. This paper gives an overview of DiaGen, our generator for diagram editors. An editor for a certain kind of diagrams is generated from a specijication, which includes a hypergraph grammar to describe the structure of diagrams. The user of a diagram editor does not have to be concerned with the grammac but can manipulate diagrams very conveniently by direct manipulation. As an additional and important feature in the context of visual languages editors generated by DiaGen can not only be usedfor editing, but also for executing, i.e., animating diagrams.

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Motivated by applications that require mechanisms for describing the structure of object-oriented programs, adaptive star grammars are introduced, and their fundamental properties are studied. In adaptive star grammars, rules are actually schemata which, via the cloning of so-called multiple nodes, may adapt to potentially infinitely many contexts when they are applied. This mechanism makes adaptive star grammars more powerful than context-free graph grammars. Nevertheless, they turn out to be restricted enough to share some of the basic characteristics of context-free devices. In particular, the underlying substitution operator enjoys associativity and confluence properties quite similar to those of context-free graph grammars, and the membership problem for adaptive star grammars is decidable.