Chapter 3 Questions
Which of the following is NOT true about the functional dependency A → (X, Y)? A) X is functionally dependent on A. B) A determines Y. C) X and Y together determine A. D) X and Y are functionally dependent on A.
C
Which of the following is true about the functional dependency (A, B) → (C, D)? A) A is the determinant of C. B) A and B together are determined by C and D together. C) A and B together determine D. D) C and D together determine A.
C
Which of the following is true for a relation? A) Entities in a column vary as to kind. B) The order of the columns is important. C) The order of the rows is unimportant. D) More than one column can use the same name.
C
A ________ is used to limit the possible values of a foreign key. A) composite key B) surrogate key C) functional dependency D) referential integrity constraint
D
A determinant that determines all the other columns in a relation is a ________. A) record B) surrogate key C) foreign key D) candidate key
D
An artificial column added to a relation to serve as the primary key is a ________. A) composite key B) candidate key C) foreign key D) surrogate key
D
An attribute is also known as a ________. A) table B) relation C) row D) field
D
If the removal of facts about one entity results in the unintentional loss of data about another entity, this is referred to as a(n) ________. A) normalization anomaly B) insertion anomaly C) update anomaly D) deletion anomaly
D
A combination of two or more columns used to identify particular rows in a relation is a ________. A) record B) composite key C) foreign key D) surrogate key
B
Surrogate keys usually slow performance.
False
A relation can have only one candidate key.
False
A combination of one or more columns used to identify particular rows in a relation is a ________. A) record B) field C) key D) tuple
C
A row can be uniquely identified by a key.
True
A combination key is a group of attributes that uniquely identifies a row.
False
Functional dependencies can involve groups of attributes.
True
A relation is also known as a(n) ________. A) table B) tuple C) relationship D) attribute
A
Explain the concept of a surrogate key.
A surrogate key is an artificial key that is created to act as the primary key for a relation. The surrogate key is a unique, numeric value that is appended to the relation. Surrogate keys are used in situations when no suitable primary key exists within the user data, or when all available primary keys within the data are too cumbersome for an efficient design. Surrogate key values have no meaning to the users and are normally hidden on all forms, reports, and displays. Most DBMS products have the ability to automatically generate values for surrogate keys as needed.
A relation is in fourth normal form if it is in BCNF and it has no ________. A) transitive dependencies B) multivalued dependencies C) partial dependencies D) deletion dependencies
B
A relation is in third normal form (3NF) if and only if it is in 2NF and ________. A) all non-key attributes are determined by the entire primary key B) there are no non-key attributes determined by another non-key attribute C) every attribute is a candidate key D) every candidate key is a determinant
B
Saying that two entities are functionally dependent means that ________. A) the entities are always connected by a mathematical equation B) for one of the entities, if we are given the value of that entity, we can determine the value of one other entity C) for both of the entities, if we are given the value of one entity, we can determine the value of the other entity D) the functional dependency will have to be removed through normalization.
B
When designing a database, one of the candidate keys in a relation is selected as the ________. A) composite key B) primary key C) foreign key D) surrogate key
B
Distinguish between the primary key and a candidate key.
Both the primary key and a candidate key can uniquely identify the rows in a table. The primary key is the candidate key that is chosen by the database designer, working with the users, to uniquely identify rows and to represent relationships. Although any candidate key could, by definition, be selected to act as the primary key, the choice of primary key is often based on design decisions such as the amount of foreign key data that would be generated.
A key consisting of one or more columns that is a primary key in another relation is a ________. A) composite key B) candidate key C) foreign key D) surrogate key
C
In the functional dependency shown as A → B, B is the determinant.
False
Explain the essence of normalization that is implemented through the use of normal forms.
The essence of normalization is to create relations that contain data on a single theme, and for each row in a relation to contain all the data about that theme for a given entity. This essence is implemented in the normal forms by taking a relation that contains data on more than one theme and splitting it into multiple relations that each contains data on a single theme. The different normal forms protect against the occurrence of modification anomalies. In practice, making sure all relations are in Boyce-Codd Normal Form (BCNF), or in Fourth Normal Form (4NF) if multivalued dependencies are found, insures high reliability of the database.
A relation is in 4NF when multivalued dependencies are isolated in their own relation.
True
Which of the following is not true about a relation? A) Has rows containing data about an entity B) Has columns containing data about attributes of the entity C) Has cells that hold only a single value D) Can have two identical rows
D
When designing or normalizing relations, each relation should have only one theme.
True
Domain/key normal form requires that every constraint be a logical consequence of the definition of domains and keys.
True
Every time we break up a relation during the normalization process, we may have to create a referential integrity constraint.
True
Given the functional dependency (A, B) → C, the attributes (A, B) are referred to as a composite determinant.
True
Given the functional dependency A → (B, C), then it is true that A → B and A → C.
True
If by knowing the value of A we can find the value of B, then we would say that B is functionally dependent on A.
True
In relational terms as defined by E.F. Codd, a column is called an attribute.
True
A determinant of a functional dependency may or may not be unique in a relation.
True
A key can be composed of a group of attributes taken together.
True
All relations are tables, but not all tables are relations.
True
A relation is a table that has special restrictions on it.
False
A referential integrity constraint is used to make sure the values of a foreign key match a valid value of a primary key.
True
A referential integrity constraint limits the values of a foreign key.
True
A relation is a table composed of columns and rows.
True
A relation is in 2NF if and only if it is in 1NF and all non-key attributes are determined by the entire primary key.
True
A relation is in 3NF if and only if is in 2NF and there are no non-key attributes determined by another non-key attribute.
True
A relation is in second normal form (2NF) if and only if it is in 1NF and ________. A) all non-key attributes are determined by the entire primary key B) there are no non-key attributes determined by another non-key attribute C) every attribute is a candidate key D) every candidate key is a determinant
A
Given the functional dependency (A, B) → C, then ________. A) A and B together → C B) A → C C) B → A D) Both A and B are correct
A
Having to enter facts about two entities when we want to enter facts about only one is an example of ________. A) insertion anomaly B) update anomaly C) deletion anomaly D) normalization anomaly
A
In general, each relation should have ________. A) one and only one theme B) one or more themes C) exactly two themes D) one or two themes
A
The only reason(s) for having relations is to ________. A) store instances of functional dependencies B) store equation components C) store equation results D) Both B and C are correct
A
If a relation is in BCNF, and each multivalued dependency has been moved to a relation of its own, then the first relation is in ________. A) Third Normal Form B) Boyce-Codd Normal Form C) Fourth Normal Form D) Domain/key normal form
C
Suppose that you need to update one value of the column SalesCost in a relation. The way the relation is constructed, this value actually needs to be changed in three different rows. However, you only change the value in two of the rows. You have just created a(n) ________. A) normalization anomaly B) insertion anomaly C) update anomaly D) deletion anomaly
C
A relation is in Boyce-Codd normal form (BCNF) if and only if it is in 3NF and ________. A) all non-key attributes are determined by the entire primary key B) there are no non-key attributes determined by another non-key attribute C) every attribute is a candidate key D) every determinant is a candidate key
D
A relation is in domain/key normal form if ________. A) every key of the relation is a logical consequence of the definition of constraints and determinants B) every key of the relation is a logical consequence of the definition of constraints and domains C) every constraint on the relation is a logical consequence of the definition of keys and determinants D) every constraint on the relation is a logical consequence of the definition of keys and domains
D
Given the functional dependency (A, B) → C, (A, B) is a ________. A) dependent variable B) determinant C) composite determinant D) Both B and C are correct
D
If a table is designed so that every determinant is a candidate key, then that relation is in ________. A) First Normal Form B) Second Normal Form C) Third Normal Form D) Boyce-Codd Normal Form
D
A characteristic of a relation is that the rows of a relation may hold identical values.
False
A constraint that requires an instance of an entity to exist in one relation before it can be referenced in another relation is called an insertion anomaly.
False
A defining requirement for Boyce-Codd Normal Form (BCNF) is that every candidate key must be a determinant.
False
A tuple is a group of one or more columns that uniquely identifies a row.
False
Any table that meets the definition of a relation is in 2NF.
False
Candidates keys are called interlocking candidate keys when they share one or more attributes.
False
Given the functional dependency (A, B) → C, then it is true that A → C and B → C.
False
Given the functional dependency A → B, then it is necessarily true that B → A.
False
It is possible to have a relation that does not have a key.
False
Describe the requirements that a table must meet to qualify as a relation.
In order for a table to meet the requirements of a relation, it must satisfy certain conditions. First, the rows contain data about an entity or some portion of the entity. Second, the columns contain data that represent attributes of the entity. Third, each column must contain the same kind of data for all rows. Fifth, each column must have a unique name. Sixth, the cells must contain single values—no group or array values are allowed. Seventh, the order of the columns and the rows is insignificant. Finally, the rows must be unique.
Briefly describe the various tasks of the primary key.
The primary key is used for four primary tasks. First, it is used to uniquely identify the rows in a table. Second, it is used to represent rows in relationships. Third, most DBMS products use the values of the primary key to organize the storage of the relation. Finally, primary keys are used in indexes and other structures to improve performance for search operations.
Explain the steps in the process of putting a relation straight into Boyce-Codd Normal Form (BCNF).
The steps are: (1) Identify all functional dependencies in the relation. (2) Identify every candidate key in the relation. (3) Check to see if all determinants are candidate keys. a. If so, the relation is in BCNF-STOP. b. If not, then: i. Move the columns of the functional dependency of the determinant that is not a candidate key to a new relation. ii. Make the determinant of that functional dependency the primary key of the new relation. iii. Leave a copy of the determinant in the original relation as a foreign key. iv. Create a referential integrity constraint between the relations. NOTE: If there is more than one functional dependency that needs to be moved, move the functional dependency with the most columns first. (4) Repeat step (3) until you reach STOP.
Explain the terms relation, tuple, and attribute.
The terms relation, tuple, and attribute are used primarily by database theoreticians. These terms are synonymous with the terms table, row, and column, respectively, in regards to a relational database. They are also equivalent to the terms file, record, and field, which tend to be used by many traditional data processing professionals.
Explain the concept of a foreign key
To implement a relationship within a relational database, the primary key of one relation is placed as an attribute in another relation. This attribute is called a foreign key in the second relation because it is the primary key of a relation that is foreign to the table in which the field resides.
A candidate key is one of a group of keys that may serve as the primary key in a relation.
True
A characteristic of a relation is that the cells of the relation hold a single value.
True
A deletion anomaly exists when deleting data about one entity results in the loss of data about another entity.
True
A foreign key is one or more columns in one relation that also is the primary key in another table.
True
A functional dependency is a relationship between attributes such that if we know the value of one attribute, we can determine the value of the other attribute.
True
A key is a combination of one or more columns that is used to identify particular rows in a relation.
True
A multivalued dependency exists when a determinant is matched to a set of values.
True
A primary key is a candidate key that has been selected to uniquely identify rows in a relation.
True
A relation is in 4NF if it is in BCNF and it has no multivalued dependencies.
True
A relation is in Boyce-Codd Normal Form (BCNF) if and only if it is in 3NF and every determinant is a candidate key.
True
A relation that is in domain/key normal form is assured to be free from all anomalies.
True
A surrogate key is an artificial column that is added to a relation to be its primary key.
True
An attribute is considered to be a non-key attribute when it is a non-prime attribute, which means that the attribute is not contained in any candidate key.
True
Any table that meets the definition of a relation is said to be in first normal form (1NF).
True
Attribute Y is functionally dependent on attribute X if the value of attribute X determines the value of Y.
True
In functional dependencies, the attribute whose value is known or given is referred to as the determinant.
True
What is a functional dependency? Give an example not used in the text.
We say that a functional dependency exists when the value of one or more attributes determines the value of another attribute. For example, suppose we have a six-sided die numbered and colored as follows: Number Color 1 Red 2 Blue 3 White 4 Green 5 Green 6 Green In this case, Number functionally determines Color, written as Number → Color. Then, if we know the Number is 3, we know the Color is White. Note that the reverse is not true—Color does not determine Number since if we are given the Color Green the number could be 4, 5, or 6. The attribute on the left-hand side of the dependency is called the "determinant." Thus, Number is a determinant. Although equations can be expressed as functional dependencies [as when the equation TotalCost = NumberSold * ItemCost is written as the functional dependency (NumberSold, ItemCost) → TotalCost] functional dependencies are not equations. Also note that a determinant can have more than one attribute [as does (NumberSold, ItemCost) in the last example] and when it does it is called a composite determinant.
A tuple is also known as a ________. A) table B) relation C) row D) field
C
The columns of a relation are sometimes called tuples.
False
In relational terms as defined by E.F. Codd, a row is called a tuple.
True
The functional dependency noted as A → B means that the value of A can be determined from the value of B.
False
If a table meets the minimum definition of a relation, it has an effective or appropriate structure.
Fasle
Explain the relationships among primary keys and functional dependencies.
Relations store instances of functional dependencies in their rows. All primary keys represent a functional dependency, since each primary key functionally determines the entire row. Since the primary key determines the entire row, if a primary key were duplicated in a relation, then the entire row would have to be duplicated. Since a relation can contain no duplicate rows, the primary key must be unique.
Relations are classified into normal forms based on the types of modification anomalies that they are vulnerable to.
True
Surrogate keys are normally not shown on forms or reports.
True
The condition that a non-key attribute determines another non-key attribute is known as transitive dependency.
True
The essence of normalization is taking a relation that is not in BCNF and breaking it into multiple relations such that each one is in BCNF.
True
The multivalued dependency noted as A → → B, means that the value of A determines a set of values of B.
True
Undesirable consequences of changing the data in relation are called modification anomalies.
True
A table that meets the definition of a relation is in ________. A) First Normal Form B) Second Normal Form C) Third Normal Form D) Boyce-Codd Normal Form
A
Given the functional dependency A → (B, C), A is a(n) ________. A) independent variable B) dependent variable C) determinant D) composite determinant
C
Referential integrity constraints are used to limit the possible values of a ________. A) composite key B) candidate key C) foreign key D) surrogate key
C
