Chapter 3 Flashcards
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.
True
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.
False
Numeric data are data on which you can perform meaningful arithmetic procedures.
True
Each table in a relational database must have a primary key.
True
In a relational model, if A determines B, C, and D, you write A = B, C, D.
False
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).
True
There is never a good reason to use null values in a database.
False
Tables within a database share common attributes that enable the tables to be linked together.
True
RDBMSs enforce integrity rules automatically.
True
The SELECT operator yields a vertical subset of a table.
False
The DIFFERENCE operator subtracts one table from the other.
True
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.
True
Which of the following is used to select partial table contents?
SELECT
FROM
BY ;
LIST
FROM
BY ;
-SELECT
FROM
WHERE ;
LIST
FROM
WHERE ;
Which query will output the table contents when the value of V_CODE is not equal to 21344?
-SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE
FROM PRODUCT
WHERE V_CODE <> 21344;
SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE
FROM PRODUCT
WHERE V_CODE <= 21344;
SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE
FROM PRODUCT
WHERE V_CODE = 21344;
SELECT P_DESCRIPT, P_INDATE, P_PRICE, V_CODE
FROM PRODUCT
WHERE V_CODE => 21344;
Which query will output the table contents when the value of the character field P_CODE is alphabetically less than 1558-QW1?
-SELECT P_CODE, P_DESCRIPT, P_QOH, P_MIN, P_PRICE
FROM PRODUCT
WHERE P_CODE
You can think of a table as a persistent representation of a logical relation.
True
The order of the rows and columns is important to the DBMS.
False
Character data can contain any character or symbol intended for mathematical manipulation.
False
The idea of determination is unique to the database environment.
False
Only a single attribute, not multiple attributes, can define functional dependence.
False
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.
True
Depending on the sophistication of the application development software, nulls can create problems when functions such as COUNT, AVERAGE, and SUM are used.
True
A foreign key must exist in both tables that have a relationship.
False
Referential and entity integrity are two names for the same thing.
False
Tables must have the same attribute characteristics (the columns and domains must be compatible) to be used in a UNION.
True
The DIFFERENCE operator subtracts one table from the other.
True
In a natural join, the column on which the join was made occurs twice in the new table.
False
The DIVIDE operation uses one single-column table (e.g., column “a”) as the divisor and one two-column table (e.g., columns “a” and “b”) as the dividend.
True
A data dictionary contains metadata—data about data.
True
A data dictionary is sometimes described as “the database designer’s database” because it records the design decisions about tables and their structures.
True
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.
False
As rare as 1:1 relationships should be, certain conditions absolutely require their use.
True
DBMSs use indexes for many different purposes.
True
____ logic, used extensively in mathematics, provides a framework in which an assertion (statement of fact) can be verified as either true or false.
Predicate
The relational database model enables you to view data ____ rather than ____.
Logically, physically
A(n) ____ is perceived as a two-dimensional structure composed of rows and columns.
Table
Date attributes contain calendar dates stored in a special format known as the ____ date format.
Julian
____ data can have only a true or false (yes or no) values.
Logical
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.
determines
The attribute B is ____ the attribute A if each value in column A determines one and only one value in column B.
functionally dependent on
Any attribute that is part of a key is known as a ____.
key attribute
No data entry at all is known as a(n) ____.
null
Controlled ____ makes a relational database work.
redundancy
Referential ____ means that if the foreign key contains a value, that value refers to an existing valid tuple (row) in another relation.
integrity
A ____ key can be described as a superkey without unnecessary attributes, that is, a minimal superkey.
candidate
All primary key entries are unique, and no part of a primary key may be ____.
null
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.
entity
To be considered minimally relational, the DBMS must support the key relational operators ____, PROJECT, and JOIN.
SELECT
____, also known as RESTRICT, yields values for all rows found in a table that satisfy a given condition.
SELECT
____ yields a vertical subset of a table.
PROJECT
____ yields only the rows that appear in both tables.
INTERSECT
A(n) ____ join links tables by selecting only the rows with common values in their common attribute(s).
natural
The equijoin takes its name from the comparison operator ____ used in the condition.
=
A(n) ____ join only returns matched records from the tables that are being joined.
inner
A ____ contains at least all of the attribute names and characteristics for each table in the system.
data dictionary
The ____ is actually a system-created database whose tables store the user/designer-created database characteristics and contents.
system catalog
In a database context, a(n) ____ indicates the use of different names to describe the same attribute.
synonym
The ____ relational type is the “relational model ideal.”
1:M
The ____ relationship should be rare in any relational database design.
1:1
Another name for a composite entity is a ____ entity.
bridge
A(n) ____ is an ordered arrangement of keys and pointers.
index
When you define a table’s primary key, the DBMS automatically creates a(n) ____ index on the primary key column(s) you declared.
unique
Codd’s Rule of ____ states:
If the system supports low-level access to the data, users must not be allowed to bypass the integrity rules of the database
Nonsubversion
