Implementation of the Object-Oriented Data Model TM. - Hennie J. Steenhagen; Peter M. G. Apers (Query Processing for Advanced Database Systems, 1991)

Optimization of Nested Queries in a Complex Object Model. - Hennie J. Steenhagen; Peter M. G. Apers; Henk M. Blanken (EDBT, 1994)

From Nested-Loop to Join Queries in OODB. - Hennie J. Steenhagen; Peter M. G. Apers; Henk M. Blanken; Rolf A. de By (VLDB, 1994)

Optimization of Object Query Languages. - Hennie J. Steenhagen (1995)

Translating OSQL-Queries into Efficient Set Expressions. - Hennie J. Steenhagen; Rolf A. de By; Henk M. Blanken (EDBT, 1996)