Christian Altenschmidt Joachim Biskup Jürgen Freitag Barbara Sprick Weakly Constraining Multimedia Types Based on a Type Embedding Ordering. 121-129 http://link.springer.de/link/service/series/0558/bibs/1508/15080121.htm 1998 conf/mis/1998 Multimedia Information Systems db/conf/mis/mis98.html#AltenschmidtBFS98