Limin Liu Zhiwei Xu Wei Li A Layered Grid User Expression Model in Grid User Management. 1055-1058 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3033&spage=1055 2003 conf/gcc/2003-2 GCC (2) db/conf/gcc/gcc2003-2.html#LiuXL03