COSC 61 Review Questions and Answers Graded A+

COSC 61 Review Questions and Answers Graded A+ 1) The identifier of the entity becomes the ________ of the corresponding table. A) primary key B) foreign key C) supertype D) subtype - Answers a 2) The ideal primary key is ________. A) short B) numeric C) fixed D) A and B E) A, B, and C - Answers e 3) A surrogate key should be considered when ________. A) a relationship is M:N B) a composite key is required C) the key contains a lengthy text field D) the key contains a number E) an index needs to be created - Answers c 4) Which of the following is not true about surrogate keys? A) They are identifiers that are supplied by the system, not the users. B) They have no meaning to the users. C) They are non-unique within a table. D) They can be problematic when combining databases. E) The DBMS will not allow their values to be changed. - Answers c 5) One of the important properties of a column is whether or not it is ________. A) found in more than one entity B) required C) character or numeric D) subject to normalization E) subject to denormalization - Answers b 6) In a relational database design, all relationships are expressed by ________. A) creating a primary key B) creating a foreign key C) creating a supertype D) creating a subtype E) creating a line between entities - Answers b 7) Which of the following would be a reason to denormalize a relation? A) Relax security B) Lack of design time C) End user preference D) Improve performance E) None of the above - Answers d 8) Which of the following is true about representing a weak entity with the relational model? A) If the weak entity is existence-dependent, the key of the parent must be part of the key of the weak entity. B) If the strong entity has a minimum cardinality of 1, the key of the weak entity must be part of the strong entity. C) If the weak entity is ID-dependent, the key of the weak entity must be part of the key of the parent entity. D) If the weak entity is ID-dependent, the key of the parent entity must be part of the key of the weak entity. E) If the parent entity is existence-dependent, then the minimum cardinality of the weak entity is zero. - Answers d 9) Which of the following is true when representing a 1:1 binary relationship using the relational model? A) The key of the entity with the highest minimum cardinality must be placed in the other entity as a foreign key. B) The key of each entity must be placed in the other as a foreign key. C) The key of either entity is placed in the other as a foreign key. D) The key of the entity with the most attributes must be placed in the other entity as a foreign key. E) Both entities must have the same primary key. - Answers c In relational algebra, σ eliminates ??? while Π eliminates ??? A. columns, rows B. rows, tuples C. rows, columns D. duplicates, columns E. tuples, nulls - Answers c Which of the following describe situations where a composite primary key is particularly useful. A. When any or all of the parts of the composite key can be NULL. B. When one of the parts is guaranteed to be UNIQUE C. As identifiers of composite entities, in which each primary key combination is allowed only once in the M:N relationship. D. As identifiers of weak entities, in which the weak entity has a strong identifying relationship with the parent entity. E. CandD - Answers e When might an attribute that seems to be the most natural choice as a primary key in a relation be found unusable as a primary key? A. when it isn't unique. B. when it isn't numeric. C. when it isn't mentioned in the business rules. D. both A and C