In the design of the persistent storage, a mapped region in main memory can suitably be called a window. Windows are exclusively used for referencing all the objects in the persistent storage. The analogy of a bookshelf and a desk (See Section 2.1) still provides a reasonable depiction of the persistent storage. However, the behavior of mapped windows has some peculiarities as compared with file binders in the analogy.
One of the peculiarities comes from synchronization, which has already been discussed above. The essence is the fact that digital objects are cloneable without modifying the original objects.
Another comes from window overlapping. Window overlapping is an inevitable consequence of dynamic allocation and reference of persistent objects. As overlapped pages of windows are mapped in the same physical memory (See Section 2.3.3), any modification in one of the pages is instantly mirrored to all the other pages.
This quality together with unallocated regions of windows sometimes results in redundant windows which are removable without any loss of information in main memory.