Chuan-Heng Ang Tok Wang Ling Xiao Ming Zhou Qualitative Spatial Relationships Representation IO&T and its Retrieval. 270-279 http://link.springer.de/link/service/series/0558/bibs/1460/14600270.htm 1998 conf/dexa/1998 DEXA db/conf/dexa/dexa98.html#AngLZ98