Transitive Closure Algorithms for Very Large Databases. - Joachim Biskup; Holger Stiefeling (WG, 1988)

An Extension of SQL for Querying Graph Relations. - Joachim Biskup; Uwe Räsch; Holger Stiefeling (Comput. Lang., 1990)

Evaluation strategies for a subclass of recursive database queries. - Holger Stiefeling (1991)

Evaluation of Upper Bounds and Least Nodes as Database Operations. - Joachim Biskup; Holger Stiefeling (FODO, 1993)