Analysing, Profiling and Optimising Orthogonal Persistence for Java by Roberto Zicari · Published January 1, 1997 · Updated February 19, 2014 Quintin Cutts, Antony Hosking LINK (PDF)
The Object-Relational Impedance Mismatch January 1, 2002 by Roberto Zicari · Published January 1, 2002 · Last modified February 18, 2014