The practical significance of taking the logical view of a database is that it serves as a reminder of the simple file concept of data storage.
You can think of a table as a persistent representation of a logical relation.
Because the relational model uses attribute values to establish relationships among tables, many database users correctly assume that the term relation refers to such relationships.
The order of the rows and columns is important to the DBMS.
Numeric data are data on which you can perform meaningful arithmetic procedures.
Character data can contain any character or symbol intended for mathematical manipulation.
Each table in a relational database must have a primary key.
A proper understanding of the concept and use of keys in a relational database model is very important.
If A determines B, C, and D, you write A = B, C, D.
Only a single attribute, not multiple attributes, defines functional dependence.
If the attribute (B) is functionally dependent on a composite key (A) but not on any subset of that composite key, the attribute (B) is fully functionally dependent on (A).
A null is created when you press the Enter key or the Tab key to move to the next entry without making a prior entry of any kind.
There is never a good reason to use null values in a database.
Depending on the sophistication of the application development software, nulls can create problems when functions such as COUNT, AVERAGE, and SUM are used.
Tables within a database share common attributes that enable the tables to be linked together.
A foreign key must exist in both tables that have a relationship.
All RDBMSs enforce integrity rules automatically.
Referential and entity integrity are two names for the same thing.
Tables must have the same attribute characteristics (the columns and domains must be identical) to be used in a UNION.
The DIFFERENCE operator subtracts one table from the other.
The SELECT operator yields a vertical subset of a table.
In a natural join, the column on which the join was made occurs twice in the new table.
A left outer join on tables CUSTOMER and AGENT yields all of the rows in the CUSTOMER table, including those that do not have a matching value in the AGENT table.
The DIVIDE operation uses one single-column table (i.e. column "a") as the divisor and one two-column table (i.e. columns "a" and "b") as the dividend.
A data dictionary contains metadata—data about data.
A data dictionary is sometimes described as "the database designer’s database" because it records the design decisions about tables and their structures.
Current relational database software generally provides only a system catalog (and not a data dictionary).
The one-to-many (1:M) relationship is easily implemented in the relational model by putting the foreign key of the "1" side in the table of the "many" side as a primary key.
As rare as 1:1 relationships should be, certain conditions absolutely require their use.
DBMSs use indexes for many different purposes.
____ logic, used extensively in mathematics, provides a framework in which an assertion (statement of fact) can be verified as either true or false. a. Predicate b. Database c. Relational d. Index
The relational database model enables you to view data ____ rather than ____. a. relationally, hierarchically b. hierarchically, relationally c. physically, logically d. logically, physically
d. logically, physically
The relational model’s creator, E. F. Codd, used the term relation as a synonym for ____. a. index b. key c. table d. reationship
A(n) ____ is perceived as a two-dimensional structure composed of rows and columns. a. table b. rowset c. attribute d. intersection
Date attributes contain calendar dates stored in a special format known as the ____ date format. a. Epoch b. Calendar c. Julian d. logical
____ data can have only a true or false (yes or no) condition. a. Logical b. Character c. Date d. Numeric
In the relational model, ____ are important because they are used to ensure that each row in a table is uniquely identifiable. a. relations b. keys c. indexes d. logical structures
In the context of a database table, the statement "A ____ B" indicates that if you know the value of attribute A, you can look up the value of attribute B. a. contains b. is related to c. owns d. determines
The attribute B is ____ the attribute A if each value in column A determines one and only one value in column B. a. logically dependent on b. owned by c. determined by d. functionally dependent on
d. functionally dependent on
Any attribute that is part of a key is known as a ____. a. key attribute b. logical attribute c. key determiner d. selector
a. key attribute
If the attribute (B) is functionally dependent on a composite key (A) but not on any subset of that ____ key, the attribute (B) is fully functionally dependent on (A). a. foreign b. unique c. composite d. complete
A ____ is any key that uniquely identifies each row. a. superkey b. special c. selective d. candidate
No data entry at all is known as a(n) ____. a. nil b. null c. empty d. zero
Controlled ____ makes a relational database work. a. relations b. logic c. chaos d. redundancy
A ____ is a textual representation of the database tables where each table is listed by its name followed by the list of its attributes in parentheses. a. relational dictionary b. logical schema c. relational schema d. data dictionary
c. relational schema
In the following table description, ____ is the primary key. PRODUCT (PROD_CODE, PROD_DESCRIPT, PROD_PRICE, PROD_ON_HAND, VEND_CODE) a. PROD_DESCRIPT b. PROD_CODE c. PROD_PRICE d. PROD_ON_HAND
Referential ____ means that if the foreign key contains a value, that value refers to an existing valid tuple (row) in another relation. a. integrity b. uniqueness c. direction d. relations
A ____ key is defined as a key that is used strictly for data retrieval purposes. a. lookup b. foreign c. candidate d. secondary
A ____ key is a minimal (irreducible) superkey. a. secondary b. candidate c. primary d. foreign
All primary key entries are unique, and no part of a primary key may be ____. a. zero b. a foreign key c. null d. a candidate key
A CUSTOMER table’s primary key is CUS_CODE. The CUSTOMER primary key column has no null entries, and all entries are unique. This is an example of ____ integrity. a. entity b. referential c. complete d. null
The ____ constraint can be placed on a column to ensure that every row in the table has a value for that column. a. HAS VALUE b. NOT NULL c. MUST HAVE VALUE d. NOT EMPTY
b. NOT NUL
To be considered minimally relational, the DBMS must support the key relational operators ____, PROJECT, and JOIN. a. INTERSECT b. UNION c. DIFFERENCE d. SELECT
____ combines all rows from two tables, excluding duplicate rows. a. INTERSECT b. UNION c. DIFFERENCE d. SELECT
____ yields only the rows that appear in both tables. a. INTERSECT b. UNION c. DIFFERENCE d. SELECT
____, also known as RESTRICT, yields values for all rows found in a table that satisfy a given condition. a. INTERSECT b. UNION c. DIFFERENCE d. SELECT
____ yields a vertical subset of a table. a. PROJECT b. SELECT c. UNION d. DIFFERENCE
A(n) ____ join links tables by selecting only the rows with common values in their common attribute(s). a. equal b. unique c. foreign d. natural
The equijoin takes its name from the comparison operator ____ used in the condition. a. * b. c. = d. >
In an outer join, the matched pairs would be retained and any unmatched values in the other table would be left ____. a. in another table b. null c. out of the results d. with matching values from the original table
A ____ contains at least all of the attribute names and characteristics for each table in the system. a. data dictionary b. relational schema c. logical schema d. join
a. data dictionary
The ____ is actually a system-created database whose tables store the user/designer-created database characteristics and contents. a. meta dictionary b. schema c. data dictionary d. system catalog
d. system catalog
In a database context, the word ____ indicates the use of the same attribute name to label different attributes. a. redundancy b. homonym c. duplicate d. synonym
In a database context, a(n) ____ indicates the use of different names to describe the same attribute. a. entity b. duplicate c. synonym d. homonym
____ relational type is the "relational ideal." a. 1:1 b. 1:M c. M:1 d. M:N
The ____ relationship should be rare in any relational database design. a. 1:1 b. 1:M c. M:1 d. M:N
Since it is used to link the tables that originally were related in a M:N relationship, the composite entity structure includes—as foreign keys—at least the ____ keys of the tables that are to be linked. a. composite b. super c. primary d. unique
A(n) ____ is an ordered arrangement of keys and pointers. a. table b. superkey c. relationship d. index
When you define a table’s primary key, the DBMS automatically creates a(n) ____ index on the primary key column(s) you declared. a. key b. incomplete c. unique d. primary
Codd’s rule of ____ states: Application programs and ad hoc facilities are logically unaffected when changes are made to the table structures that preserve the original table values (changing order of column or inserting columns). a. Nonsubversion b. Logical Data Independence c. Comprehensive Data Sublanguage d. Integrity Independence
b. Logical Data Independence
The logical view of the relational database is facilitated by the creation of data relationships based on a logical construct known as a(n) ____________________.
In the relational model, ____________________ are important because they are used to ensure that each row in a table is uniquely identifiable.
Attribute A determines attribute B (that is, B is functionally ____________________ on A) if all of the rows in the table that agree in value for attribute A also agree in value for attribute B.
A(n) ____________________ key can be described as a superkey without unnecessary attributes.
If the foreign key contains either matching values or nulls, the table that makes use of that foreign key is said to exhibit ____________________ integrity
The following example exhibits ____________________ integrity: The CUSTOMER table’s primary key is CUS_CODE. The CUSTOMER primary key column has no null entries, and all entries are unique. Similarly, the AGENT table’s primary key is AGENT_CODE, and this primary key column also is free of null entries.
To avoid nulls, some designers use special codes, known as ____________________, to indicate the absence of some value.
The relational operators have the property of ____________________; that is, the use of relational algebra operators on existing tables (relations) produces new relations.
PRODUCT yields all possible pairs of rows from two tables—also known as the ____________________ product.
____________________ is the real power behind the relational database, allowing the use of independent tables linked by common attributes.
A(n) ____________________ links tables on the basis of an equality condition that compares specified columns of each table.
____________________ joins are especially useful when you are trying to determine what value(s) in related tables cause(s) referential integrity problems.
A(n) ____________________ provides a detailed description of all tables found within the user/designer-created database.
The ____________________ catalog can be described as a detailed system data dictionary that describes all objects within the database, including data about table names, the table’s creator and creation date, the number of columns in each table, the data type corresponding to each column, index filenames, index creators, authorized users, and access privileges.
The ____________________ relationship is the relational database norm.
If one department chair—a professor—can chair only one department and one department can have only one department chair, then the entities PROFESSOR and DEPARTMENT exhibit a(n) ____________________ relationship.
____________________ relationships can be implemented by creating a new entity in 1:M relationships with the original entities.
Fortunately, the problems inherent in the ____________________ relationship can easily be avoided by creating a composite entity.
The proper use of ____________________ keys is crucial to controlling data redundancy.
Proper data ____________________ design requires carefully defined and controlled data redundancies to function properly.
A(n) ____________________ is an orderly arrangement used to logically access rows in a table.
A(n) ____________________ index is an index in which the index key can have only one pointer value (row) associated with it.
The index key can have multiple attributes, this is called a(n) ____________________ index.
Codd’s rule of ____________________ states that every value in a table is guaranteed to be accessible through a combination of table name, primary key value, and column name.