Towards distributed graph grammars. - Paul Boehm; Hartmut Ehrig; Udo Hummert; Michael Löwe (Graph-Grammars and Their Application to Computer Science, 1986)

Towards algebraic data types grammars: a junction between algebraic specification and graph grammars. - Hartmut Ehrig; Annegret Habel; Udo Hummert; Paul Boehm (Bull. EATCS, 1986)

Algebraische Theorie von High-Level-Netzen. - Udo Hummert (1989)

Semantics, composition and net properties of algebraic high-level nets. - Christian Dimitrovici; Udo Hummert; Laure Petrucci (Applications and Theory of Petri Nets, 1990)