1. (1 point) What technique is used to model the situation that Student may be f
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Question
1. (1 point) What technique is used to model the situation that Student may be friends of other students? A) Gerund B) Weak entities C) Super/sub types D) Recursive relationships
2. (1 point) I used email as the primary key for customers. A customer calls in to change his email but my database does not allow me to do. Why? A) The email address is in PK column. Changing it requires to erase it first and then enter a new value. A PK column cannot be empty at any point in time B) The email address is unique and so it cannot be changed C) The email address appears in other places as foreign key values. The change will result in violations of referential integrity D) The new email address may be too small in size to enter.
3. (1 point) What technique is used to model the situation that Student may have multiple addresses? A) Associative Entity (gerund) B) Weak entities C) Super/sub types D) Recursive relationships
4. (1 point) What is not right about weak entities? A) often used to model multivalued attributes B) do not have a full UID themselves C) must have 1:m relationships with a strong entity D) cannot exist independently of a strong entity
5. (1 point) (check all that apply) When do you use recursive relationships? A) the relationship between employees and their supervisors B) the relationship between employees and their dependents C) the relationship between employees and their departments D) the relationship between employees and their team members E) the relationship between employees and their job assignments
6. (1 point) When do you use gerunds? A) when there are data about relationships B) when there exist m:m relationships between two entities C) when there is a need to treat a relationship as an enity D) All of the above
7. (1 point) Use of a supertype/subtype relationship is necessary when which of the following exists?A) An instance of a subtype participates in a relationship that is unique to that subtype. B) An instance of a subtype participates in a relationship that is the same as the other subtypes. C) Attributes apply to all of the instances of an entity type. D) No attributes apply to any of the instances of an entity type.
8. (1 point) The ER model for a small bank system has Customer, Account, Checking Account, Employee, Check, Transactions, etc. as entities. Which of the following is correct use of subtypes? A) Check is a subtype of Checking Account B) Checking Account is a subtype of Account C) Transaction is a subtype of Account D) Employee is a subtype of customers
9. (1 point) (check all that apply) The ER model for a small bank system has Customer, Account, Checking Account, Employee, Check, Transactions, etc. as entities. Which of the following is correct use of recursive relationships? A) Checking account is a special kind of checks B) related bank transfers as one for credit and one for debit C) Checks belong to a checking account D) Employees and their supvervisors
10. (1 point) In the ER model for a library checkout system, the involved entities include Book, BookCopy, Patron, Checkout, Return, Reservation, Employee, and Transaction. Assume patrons can reserve multiple books but have the choice to indicate which book of is of higher or lower priority. Where do you indicate so? A) Reservation B) Gerund between Patron and BookCopy C) Gerund bewteen Patron and Book D) Gerund between Reservation and BookCopy E) Gerund between Reservation and Book
Explanation / Answer
1. D. Recursive relationships
A. A unary relationship is when both participants in the relationship are the same entity.
B. Recursive relationships occur within unary relationships. A recursive association connects a single class type (serving in one role) to itself (serving in another role).
Here Entity is Student and relation is friend. One student can have many friends and one student can be friends of many Students.
Since Entity is single that is Student , this is a Unary relation. Here the relation is M:N.
2.C.The email address appears in other places as foreign key values. The change will result in violations of referential integrity
For PK, we can update any PK at any time as long as the new value entered is not already there for PK column in any row of the table.
The problem arises when we have referential integrity, that is when some other column of different table is referring to PK of the first table.
3. A) Associative Entity (gerund)
Here we have 3 Entities - Student, Address and one more table which will have composite key (Student Id , Address Id)
4. A) often used to model multivalued attributes
5.A) the relationship between employees and their supervisors
D) the relationship between employees and their team members
Recursive relationships occur within unary relationships
Since in both A and D the both the parties in relationship are same Entity.
in option A, supervisors are also Employee- Entity is Employee.
in option B, team members are also employee.
6. A) when there are data about relationships
7.
8.B) Checking Account is a subtype of Account
Account is a Parent Account and Checking Account is a subtype.
9.D) Employees and their supvervisors
10.
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