For the battleships database schema defined above in question 4, write the following as tuple-based CHECK constraints. (a) No ship can be in battle before it is launched.

Create a database Entity and Relationship Diagram (ERD) for the following application (Submitted An image of the Diagram By using Any Application:The Application idea: It is a mobile application called (Khair) to help people. This assistance is moral, material. This assistance is also provided by good people in our community. Example to understand the Application idea more: For example, a person urgently needs a medical chair or bed and does not have the ability to purchase what he needs. The medical chair or bed is requested through the application, and whoever has what he requests initiates the request through the application’s messages and determines the meeting place. Application models (page): Login included: login registration login included: user name password New registration included: name E-mail Password phone number date National Identification Number Home page included: Request - applicant name - address - send message Messages list form included: list of users Messager…

The database used for this question is a very simple one with the following schema: (Primary keys are bold, foreign keys are underlined)   CUSTOMER (CustID, FirstName, LastName, City, Phone, Email) INVOICE (InvoiceNumber, CustID, Date) INVOICE_ITEM(InvoiceNumber, ItemNumber, Quantity) ITEM (ItemNumber, ItemName, UnitPrice)   When a customer makes a purchase, an invoice is created. The invoice may be for many items. For example, in a single purchase, a customer might buy 10 Back Scratchers, 4 Hair Removers and a Dog Lead. Provide relational algebra (NOT SQL) queries to find the following information. Each question is worth 2 marks. NOTE: You can use the symbolss, P, etc., or the words’ PROJECT’, ‘RESTRICT’etc.as you prefer. You do not need to try to make efficient queries – just correct ones. Where you use a join, always show the join condition.   List the first and last names of Customers who come from the City named Perth. List the first and last names of customers who had…

Topic : Database Systems Please follow the picture form answer these question!   Vis Library is a multi-categories book library that provides a wide range of genres from kids books to special braille books. The customers can read the books on-site or choose a delivery service. As a database designer, they want you to design and implement a database to support their business.  At the initial meeting to discuss the database design, the following requirements were gathered:  A new customer is required to register the account, pick the membership type, and pay the necessary cost. The systems must be able to manage the detailed information of each member. There are two membership types: silver dan gold. This membership is necessary to borrow books and read on the spot. Silver membership can be obtained by showing the id card and filling the registration form without any cost. On the other hand, Rp 20000 registration costs and Rp 10000 monthly costs are needed to get a gold membership. Gold…