It is basic simulation that process Library Environment. In the Library, there are books with limited amount to be requested by students. Students which is registered to library go to the library for requesting to borrow a book. When a student requests a book that is available, she/he can borrow immediately. If not, a student needs to wait for demand queue or another student to give the book back. However, there is special membership called gold membership that enables students to borrow without waiting for the queue.
Diagram for Process