@incollection{Gott98a,
author = {G.~Gottlob AND M.~Schrefl},
booktitle = {{Semantics in Databases}},
editor = {B.~Thalheim AND L.~Libkin},
pages = {92--113},
publisher = {Springer Verlag},
series = {Lecture Notes in Computer Science, LNCS Vol.\ 1358},
title = {{The Evolving Algebra Semantics of Class and Role Hierarchies}},
year = {1998}
}