In the HELP menu from ILWIS there´s all the information you need but I post here the information from the help menu related with Object Collections:
"An object collection is a set of ILWIS objects. An
object collection only stores the names and locations of the object
definition files of the maps, tables, etc. that are included in the object
collection. The object definition files of these maps, tables, etc. contain
further references to the names and locations of the data files on disk.
can be created to organize your data as 'projects';
can be the result of import when only ILWIS object definition files are
created while the data files remain in their native format and in their original
This dialog box appears when:
in the Main window, you choose the Create Object
Collection command from the File
in the Operation-tree,
you open the Create item, and select the New Object Collection command, or
in the Operation-list,
you double-click the New Object Collection command.
Optionally, type a description for the object collection. The
description is visible on the status bar of
the Main window when moving the mouse pointer over the object collection in a Catalog.
The new object collection will be opened as a new Catalog.
You can add objects to the object collection by selecting
objects in another Catalog, then drag these objects to the object collection.
You can also select objects in another Catalog and then use Copy and Paste.