Chapter 6 Flashcards
The first step in the database design process is to create tables and columns from entities and attributes.
True
When creating a relational database design from E-R diagrams, first create a relation for each relationship.
False
Each entity in the extended E-R model is represented as a table in the relational database design.
True
An entity needs to be examined according to normalization criteria before creating a table from it in the relational database design.
False
When creating a table in the relational database design from an entity in the extended E-R model, the attributes of the entity become the rows of the table.
False
By default, the identifier of the entity becomes the foreign key of the corresponding table.
False
The ideal primary key is short, numeric, and fixed.
True
A surrogate key is appropriate when the primary key of a table contains a lengthy text field.
True
One of the important properties of an attribute is whether or not it is required
True
A surrogate key is a unique, system-supplied identifier used as the primary key of a table.
True
The values of a surrogate key have no meaning to the users.
True
A surrogate key should be considered when the key contains a lengthy text field.
True
Whether or not an attribute is required is determined during the database modeling phase.
False
A null value is an attribute value that has been set to zero.
False
Data types are consistent across all DBMS products.
False
A default value is the value the user enters into the row the first time the user enters data.
False
A data constraint is a limitation on data values.
True
The last step in creating a table is to verify table normalization.
True
One of the important properties of a column is whether or not it can have a NULL value.
True
A foreign key is a key that does not belong in any table.
False
In a relational database design, all relationships are expressed by creating a foreign key.
True
When the key of one table is placed into a second table to represent a relationship, the key is called a “relational key” in the second table.
False
To represent a 1:1 binary relationship in a relational database design, the key of one table is placed into the second table.
True
When placing a foreign key for a 1:1 relationship, the key of either table can be used as the foreign key in the other table.
True
In a 1:1 relationship, the foreign key is defined as an alternate key to make the DBMS enforce uniqueness.
True
In a 1:N relationship, the term “parent” refers to the table on the “many” side of the relationship.
False
In 1:N relationships, the table on the “one” side is called the parent.
True
In representing a 1:N relationship in a relational database design, the key of the table representing the parent entity is placed as a foreign key in the table representing the child entity
True
In representing a 1:N relationship in a relational database design, the key of the table representing the entity on the “many” side is placed as a foreign key in the table representing the entity on the “one” side of the relationship.
False
To represent a 1:N relationship in a relational database design, an intersection table is created.
False
In 1:N relationships, the table on the “many” side is called the child.
True
To represent a one-to-many relationship in a relational database design, the key of the child table is placed as a foreign key into the other table.
False
To represent an M:N relationship in a relational database design, a table is created to represent the relationship itself.
True
To represent an M:N relationship in a relational database design, an intersection table is created.
True
Which of the following is not a step in the database design process?
A) Create tables and columns from entities and attributes
B) Select primary keys
C) Represent relationships
D) Create constraints and triggers
E) All of the above are steps in the database design process
D
The first step in transforming an extended E-R model into a relational database design is to ________.
A) create a table for each relationship
B) evaluate the entities against the normalization criteria
C) create a table for each entity
D) remove any recursive relationships
E) document referential integrity constraints
C
Each attribute of an entity becomes a(n) \_\_\_\_\_\_\_\_ of a table. A) column B) primary key C) foreign key D) alternate key E) B or D
D
The identifier of the entity becomes the \_\_\_\_\_\_\_\_ of the corresponding table. A) primary key B) foreign key C) supertype D) subtype E) either A or B
A
The ideal primary key is \_\_\_\_\_\_\_\_. A) short B) numeric C) fixed D) A and B E) A, B, and C
E
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
C
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 nonunique within a table.
D) They can be problematic when combining databases.
E) The DBMS will not allow their values to be changed.
C
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
B
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
B
When representing a 1:1 relationship in a relational database design, ________.
A) the key of each table must be placed as foreign keys into the other
B) the key of either table may be placed as a foreign key into the other
C) the key of both tables must be the same
D) the intersection table gets the key from both relations
E) B and C
B
To represent a one-to-many relationship in a relational database design, ________.
A) the key of the child is placed as a foreign key into the parent
B) the key of the parent is placed as a foreign key into the child
C) an intersection table must be created
D) the key of the table on the “many” side is placed in the table on the “one” side
E) the keys of both tables are joined into a composite key
B
When representing a one-to-many relationship in a relational database design, ________.
A) the parent is always on the one side of the “one-to-many” relationship
B) the child is always on the one side of the “one-to-many” relationship
C) either parent or child can be on the one side of the “one-to-many” relationship, and the choice is arbitrary
D) either parent or child can be on the one side of the “one-to-many” relationship, and special criteria indicate which table should be on the one side
E) None of the above is correct.
A
Many-to-many relationships are represented by ________.
A) two tables with an M:N relationship
B) two tables with a 1:N relationship
C) an intersection table which has M:N relationships with the two tables
D) an intersection table which has 1:N relationships with the two tables
E) two intersection tables which each have 1:N relationships with the two tables
Answer: D
D
In many-to-many relationships in a relational database design, ________.
A) the key of the child is placed as a foreign key into the parent
B) the key of the parent is placed as a foreign key into the child
C) the keys of both tables are placed in a third table
D) the keys of both tables are joined into a composite key
E) C and D
E
In many-to-many relationships in a relational database design, ________.
A) the intersection table is ID-dependent on one of the parents
B) the intersection table is ID-dependent on both of the parents
C) the minimum cardinality from the intersection table to the parents is always M
D) A and B
E) B and C
E
In relational database design, ID-dependent entities are used to ________.
A) represent N:M relationships
B) handle associative relationships
C) handle multivalued attributes
D) handle archetype/instance relationships
E) All of the above.
E
To represent an M:N relationship in a relational database design, in essence it is reduced to two 1:N relationships.
True
The key of an intersection table is always the combination of the keys of both parents.
True
In many-to-many relationships in a relational database design, the primary keys of both tables are joined into a composite primary key in the intersection table.
True
An intersection table is always ID-dependent on both of its parent tables.
True
An intersection table can have additional attributes besides the keys of its parent tables.
False
Like all ID-dependent relationships, the parents of an association table are required.
True
Association tables sometimes connect more than two entities.
Ture
An ID-dependent table can be used to represent multivalued attributes
True
All identifying relationships are 1:N.
True
When creating a table for an ID-dependent entity, both the key of the parent and the key of the entity itself must appear in the table.
True
The design transformation for all IS-A relationships can be summarized by the phrase “place the key of the parent table in the child table.”
False
When transforming an ID-dependent E-R data model relationship into a relational database design where the child entity is designed to use a surrogate key, the relationship changes to a weak but not ID-dependent relationship.
True
When transforming supertype/subtype entities into a relational database design, an entity is created for the supertype only.
False
When transforming supertype/subtype entities into a relational database design, the key of the supertype table is placed into the subtype table typically as the key.
True
To represent an IS-A relationship in a relational database design, the IS-A relationship must be converted into a HAS-A relationship.
False
Discriminator attributes can be represented in relational designs.
False
When transforming supertype/subtype entities into a relational database design, all of the attributes for the supertype table are placed into the subtype relations.
False
When transforming an extended E-R model into a relational database design, recursive relationships are treated fundamentally the same as other HAS-A relationships.
True
Recursive M:N relationships are represented with an intersection table that shows pairs of related rows from a single table.
True
Referential integrity constraints should disallow adding a new row to a child table when the foreign key does not match a primary key value in the parent table.
True
When transforming an E-R data model into a relational database design, the key of the parent entity should be placed as part of the primary key into the child entity ________.
A) when the child entity is ID-dependent
B) when the child entity is non-ID-dependent
C) when the child entity has a 1:1 relationship with the parent entity
D) when the child entity has a 1:N relationship with the parent entity
E) when the child entity has a recursive relationship with the parent entity
A
When transforming an ID-dependent E-R data model relationship into a relational database design and the parent entity has a surrogate primary key and the child entity has a data identifier, then the primary key of the child table should be ________.
A) the parent’s surrogate key + the child’s data key
B) the parent’s surrogate key + a surrogate key in the child
C) either A or B will work, and neither way is preferable
D) either A or B will work, but method A is preferable
E) either A or B will work, but method B is preferable
E
When transforming an ID-dependent E-R data model relationship into a relational database design and the child entity is designed to use a surrogate key, then ________.
A) the parent entity must also use a surrogate key
B) the relationship remains an ID-dependent relationship
C) the relationship changes to a non-ID-dependent relationship
D) A and B
E) A and C
C
Which of the following is not true about representing subtypes in a relational database design?
A) One table is created for the supertype and one for each subtype.
B) All of the attributes of the supertype are added to the subtype relations.
C) The key of the supertype is made the key of the subtypes.
D) A subtype and its supertype are representations of the same underlying table.
E) An instance of the supertype may be related to one instance each of several subtypes.
B
In a supertype-subtype structure, discriminator attributes ________.
A) are easily represented in a relational design
B) cannot be represented in a relational design
C) require application logic to determine which subtypes correspond to a specific supertype instance
D) A and C
E) B and C
E
Which of the following is not true of recursive relationships?
A) When the recursive relationship is M:N, an intersection table is created.
B) The rows of a single table can play two different roles.
C) The techniques for representing the tables are the same as for non-recursive relationships except the rows are in the same table.
D) Recursive relationships can be 1:1, 1:N, or M:N relationships.
E) Even when the relationship is 1:N, a new table must be defined to represent the relationship.
E
Which of the following is not true of ternary relationships?
A) Can be treated as a collection of binary relationships
B) Are represented in the same way as binary relationships
C) Must involve at least one M:N relationship
D) Involve three entities of different logical types
E) Often require documentation of special considerations as business rules
C
The binary constraint MUST NOT indicates that ________.
A) a specific binary relationship must not be included in a ternary relationship
B) a table includes values that must not occur in a binary relationship
C) a table includes values that must not occur in a ternary relationship
D) a binary relationship includes value combinations that must not occur in a binary relationship
E) a binary relationship includes value combinations that must not occur in a ternary relationship
E
The binary constraint MUST COVER indicates that ________.
A) a specific binary relationship must be included in a ternary relationship
B) a table includes values that must occur in a binary relationship
C) a table includes values that must occur in a ternary relationship
D) a binary relationship includes value combinations that must occur in a binary relationship
E) a binary relationship includes a set of value combinations that must all occur in a ternary relationship
E
To which of the following actions are referential integrity constraints not applied?
A) create
B) insert
C) modify
D) delete
E) Referential integrity constraints are applied to all of the listed actions.
A
A referential integrity constraint policy that insures that foreign key values in a table are correctly maintained when there is a change to the primary key value in the parent table is called cascading changes.
False
A referential integrity constraint policy that insures that all rows containing a particular foreign key value in a table are eliminated from the table when the row containing the corresponding primary key value in a parent table is eliminated from the database is called cascading deletes.
True
When the parent entity is required (M) in a relationship, every row of the child table must have a valid, non-null value of the foreign key.
True
Cascading deletions are generally not used with relationships between strong entities.
True
Cascading deletions are generally not used with relationships for weak child entities.
False
If the parent is required, then a new child row must be created with a valid foreign key value.
True
When the parent entity has a surrogate key, the enforcement actions are the same for both parent and child.
False
When the child entity is required (M) in a relationship, there needs to be at least one child row for each parent row at all times.
True
It is easy to enforce the referential integrity actions for M-M relationships.
False
A referential integrity constraint policy that insures that foreign key values in a table are correctly maintained when there is a change to the primary key value in the parent table is called \_\_\_\_\_\_\_\_. A) incremental updates B) incremental deletes C) controlled key adjustments D) cascading updates E) cascading deletes
D
A referential integrity constraint policy that insures that all rows containing a particular foreign key value in a table are eliminated from the table when the row containing the corresponding primary key value in a parent table is eliminated from the database is called \_\_\_\_\_\_\_\_. A) incremental updates B) incremental deletes C) controlled key adjustments D) cascading updates E) cascading deletes
E
A referential integrity constraint policy that guarantees that a row in a parent table always has a required entry in a child table ________.
A) is known as a minimum cardinality enforcement action
B) needs to be documented by the database development team
C) is enforced in most DBMS products
D) A and B
E) A, B, and C
D
When transforming an ID-dependent E-R data model relationship into a relational database design, the referential integrity constraints should allow \_\_\_\_\_\_\_\_. A) parent updates to cascade B) child updates to cascade C) child deletes to cascade D) A and B E) A, B, and C
A
