@article{Gott96a,
author = {G.~Gottlob AND M.~Schrefl AND B.~R{\"o}ck},
journal = {{ACM Transactions on Information Systems (ACM TOIS)}},
number = {3},
pages = {268--296},
title = {{Extending Object-Oriented Systems with Roles}},
volume = {14},
year = {1996}
}