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
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.
True
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
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.
True
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
