Hartmut Ehrig, Hans-Jörg Kreowski: The Skeleton of Minimal Realization. Studien zur Algebra und ihre Anwendungen 7:137-154, 1979.
Hartmut Ehrig, Hans-Jörg Kreowski: Pushout-Properties: An Analysis of Gluing Constructions for Graphs. Mathematische Nachrichten 91:135-149, 1979.
Hartmut Ehrig, Hans-Jörg Kreowski: Algebraic Theory of Graph Grammars Applied to Consistency and Synchronization in Data Base Systems. In Proc. Workshop WG'78 Graphentheoretische Konzepte in der Informatik (Feuerstein 1978), volume 13 of Applied Computer Science, pages 227-244. Hanser, 1979.
Hans-Jörg Kreowski: A Pumping Lemma for Context-free Graph Languages. In Proc. International Workshop on Graph Grammars and Their Application to Computer Science and Biology (Bad Honnef, 1978), volume 73 of Lecture Notes in Computer Science, pages 270-283. Springer, 1979.
Hartmut Ehrig, Hans-Jörg Kreowski, Peter Padawitz: Algebraic Implementation of Abstract Data Types: An Announcement. SIGACT News 11:25-29, 1979.
Hartmut Ehrig, Hans-Jörg Kreowski, Herbert Weber: Neue Aspekte algebraischer Spezifikationsschemata für Datenbanksysteme. In Proc. GI-Fachtagung Formale Modelle für Informationssysteme (Tutzing 1979), volume 21 of Informatik-Fachberichte, pages 181-198. Springer, 1979.
