The Relational Model $3$: Advanced Topics $1.$ What is a view? How do you define a view? Does the data described in a view definition ever exist in that form? What happens when a user accesses a database through a view? $2.$ Using data from the BITS database, define a view named TopLevelClient. It consists of the number, name, address, balance, and credit limit of all clients with credit limits that are greater than or equal to $$10,000.$ a$.$ Using SQL$,$ write the view definition for TopLevelClient. b$.$ Write an SQL query to retrieve the number and name of all clients as well as the difference between their credit limit and balance in the TopLevelClient view. c$.$ Convert the query you wrote in Question $2$ b to the query that the DBMS will actually execute. $3.$ Define a view named ItemOrder. It consists of the TaskID, description, price, order number, order date, and quoted price for all order lines currently on file. a$.$ Using SQL$,$ write the view definition for ItemOrder. b$.$ Write an SQL query to retrieve the TaskID, description, order number, and quoted price for all orders in the ItemOrder view for items with quoted prices that exceed $$100.$ c$.$ Convert the query you wrote in Question $3$b to the query that the DBMS will actually execute. $4.$ What is an index? What are the advantages and disadvantages of using indexes? How do you use SQL to create an index?