M. Garc\'ıa-Solaco, F. Saltor, and M. Castellanos. chapter Semantic heterogeneity in multidatabase systems, Prentice Hall International (UK) Ltd., Hertfordshire, UK, UK, (1995)
J. Hereth, G. Stumme, U. Wille, and R. Wille. Conceptual Structures: Logical, Linguistic, and Computational Structures. Proc. ICCS, volume 1867 of LNAI, page 421--437. Springer, Heidelberg, (2000)