1. Design ER Model for part of Internet sales system. The system provide the sales services for many customers to order many products from many companies. All Customers, products and companies information are stored in DB. Each customer can place one or more orders. The order can contain many products that are supplied by one or more companies. 2. Design ER Model for part of a Bank databases. The bank has multiple Branches, and each branch can have multiple accounts. Each customer can has one account or more; or other services. 3. Design ER Model for Hospital databases. Each Doctor is described by Doc ID, Phone, address, and specialization. Each doctor is allowed to work in only one department. Each department is described by Dept no, Name, and is supervised by a doctor. Each patient is described by Card number, name, address, and phone. Each patient is assigned to one or more department. It's required to keep track each admission date. Each lab is described by LabNo, name. It's required to keep track any lab service that may be done to the patient. 4. Design ER Model for a library to manage data of books. The library contains books which are described by an ISBN, Title, Specialization. Each Book is published by one Publisher and written by many Authors. A publisher is described by name, ID, Address, Fax and Phone number. An author is described by name, ID, Address, Fax and Phone number. Each author writes many books