why in ICEM, we cannot create volume? why we here defining volume by closed only surfaces? while deleting surface, how can automatically delete the lines and points relate to that surface?

All the pre-processing softwares are concerned only witht the topology and not the way volume are visualized. What you may be comparing is the way ICEM represents volume with CAD software such as Unigraphics or Pro-E. By definition, a volume is a geometric entity bound by surface. Hence, ICEM is correct!

In ICEM, all geometric entities are grouped i.e. point, lines, surfaces and volumes are grouped in default groups. You can delete lower order entities automatically. You may use "Rebuild Topology" option to get rid of unwanted points and lines.

Hope this explains your query!

Amod