When we open a large PPT file or openoffice other XML file f.e.odp file, we 
will wait for a long time to see the content of the file. Conversely openning 
the same file through MS PowerPoint will be fluent a lot, almost at once we 
will see the first some pages. In OpenOffice, the pages should be shown after 
all the pages are loaded. So we can modify the current documention load 
mechanism in impress application, first of all we load the first n pages, as 
for other pages we just create empty slides, and then we will contiue to load 
other non-loaded pages in the background. So We can operate the pages which 
have been loaded at the same time other non-loaded pages can be loaded.