final 5

a

Choose the right answer: a. Duplicate-elimination operator is used to convert a bag to a set b. Duplicate-elimination operator is used to add duplicate tuple to a relation c. None of the others d. Duplicate-elimination operator is used to convert a set to a bag

a

Choose the right statement a. Basic relational algebra cannot be expressed in Datalog rule(s) b. All of the others c. Relational algebra can express recursion d. Any single safe Datalog rule can be expressed in relational algebra

a

Choose the wrong statement a. We should start the high level database design (for example, ER diagram in conceptual design) after getting user requirements. b. All of the others c. The high level database design (for example, ER diagram in conceptual design) depends on DBMS selection d. The high level database design (for example, ER diagram in conceptual design) is independent of DBMS selection.

c

Consider a relation with schema R(A, B, C, D, E) and the set of FDs: BC -> D, D -> A, A -> B. Find one key of R. a. BC b. AB c. None of the others d. BD

b

Suppose relation R(A,B,C,D) with FD's A?B, B?D, CD?A. This relation is decomposed into 3 relations S1={A,D}, S2={A,C}, S3={B,C,D}. Is this decomposition lossless join? a. Yes b. No

c

Suppose relation R1 has n1 attributes and t1 tuples, relation R2 has n2 attributes and t2 tuples, then the Cartesian Product R3 = R1 x R2 has ________ a. n1*n2 attributes, and t1*t2 tuples b. n1*n2 attributes, and t1+t2 tuples c. n1+n2 attributes, and t1*t2 tuples d. n1+n2 attributes, and t1+t2 tuples

c

The degree of a relationship is ______ a. The number of binary relationships b. The number of attributes in a relation c. The number of entities involved with the relationship d. The number of tuples in a relation

a

We should avoid redundancy when designing database because _____ a. We may encounter deletion anomalies b. All of the others c. We may encounter update anomalies d. It wastes spaces

b

When performing union, intersection, or difference operations on relations R and S, they must be type compatible. That is, ______ a. R and S must have the same number of attributes b. R and S must have the same number of attributes and the domain of corresponding attributes of R and S must be compatible c. The domain of corresponding attributes of R and S must be compatible d. The names of attributes of R and S must be the same

c

Which is not a correct name for an XML element? a. &ltNote> b. &lt1dollar> c. All of the others d. &lthav1>

c

Which of the following expression is equivalent to the intersection of R and S: a. R - S b. R - (S - R) c. R - (R - S) d. S - (R - S)

b

Which of the following is considered disadvantage of triggers? a. Triggers run every time the database fields are inserted/updated/deleted, so it adds overhead to system. b. Triggers execute invisible to client application. It is called by the database server automatically, not by the client application or user. c. All of the others d. Unlike stored procedure, parameters cannot be used with triggers.

b

Which of the followings is incorrect? a. In ODL, an attribute is represented in the class declaration b. In ODL, attributes are only integers and strings c. None of the others d. In ODL, a simplest kind of property is attribute

d

With SQL, how can you insert "Trinh" as the "LastName" in the "Persons" table? a. None of the others b. INSERT INTO Persons ('Trinh') INTO LastName c. INSERT ('Trinh') INTO Persons (LastName) d. INSERT INTO Persons (LastName) VALUES ('Trinh')

c

With SQL, how do you select all the records from a table named "Persons" where the "LastName" is alphabetically between (and including) "Nguyen" and "Tran"? a. SELECT * FROM Persons WHERE LastName>'Nguyen' AND LastName<'Tran' b. SELECT LastName>'Nguyen' AND LastName<'Tran' FROM Persons c. SELECT * FROM Persons WHERE LastName BETWEEN 'Nguyen' AND 'Tran' d. None of the others.