DATA MANAGEMENT APPLICATIONS C170
1. What is a table?: A table is a persistent representation of a logical
relation that is a relation whose contents can be saved for permanent
use.
2. What are the characteristics of a relational table?: The
characteristics of a relational table are that a table is perceived as a
two-dimensional structure composed of rows and columns, each
row (tuple) represents a single entity
occurrence within the set, each column represents an attribute, each
column has a distinct name, each intersection of a row and column
represents a single data value, all values in a column must be of the
same data format, the order of the rows and columns don't matter to
the DBMS, and
each table must have an attribute (or combination of attributes)
that uniquely identifies each row (tuple).
3. What is a tuple?: A tuple is a row that represents a single entity
occurrence within a set.
4. What are records?: A record is the same as a tuple (row).
5. What is a field?: A field is a column.
6. What is a key?: A key consists of one or more attributes that
determine other attributes. For example, a social security number
identifies all of the other attributes related to that person.
7. What is determination?: Determination is the state in which knowing
,the value of one attribute allows you to determine the value of another
attribute. For example, if you know a key, you can find other
information.
8. What is functional dependence?: Functional dependence is when
knowing the value of one or more attributes lets you know the value of
the other attributes. For example, knowing the first name and the
social security number would let you find the person's last name.
9. What is full functional dependence?: Full functional dependence is
when knowing the value of one or more attributes lets you know the
value of other attributes and the value of the known attributes are
NEEDED to find the other attributes. For example, a social security
number lets you find the first and last name of someone. This is full
functional dependence. If it was a social security number and a first
name this would just be functional dependence because the first
name is not required to look up the last name. All you need is the
SSN.
10.What is a determinant?: A determinant is an attribute whose value
deter- mines the value of other attributes. For example, a social
security number could be the determinant for your last name.
,11.What is a dependent?: A dependent is an attribute whose value is
determined by another attribute. For example, you last name could be
a dependent of your social security number.
12.What is a composite key?: A composite key is a key that is
composed of one or more attribute. For example, the key of your last
name and you social security number could be used to determine your
first name. This would be a composite key because you are using your
last name and your SSN in the key.
13.What is a superkey?: A superkey is a key that can uniquely identify
any row in a table. Some examples of this would be your social
security number identifying a row corresponding to your information,
but a superkey isn't limited to full functional dependence. Your SSN
and your last name used as a key would still be a superkey.
14.What is a candidate key?: A candidate key is a minimal super key.
This is to say it has no extra attributes. If you only need a social
security number to identify the row related to a person than the
candidate key is the SSN. A key consisting of an SSN and the last
name in this case would not be a candidate key.
15.What is entity integrity?: Entity integrity is the condition in which
each row (entity instance or tuple) in the table has it's own unique
identity. This requires that all values in the primary key be unique and
that the primary key cannot be null.
16.What is a null?: A null is the absence of a data value. A null should
be avoided whenever possible. In fact, you can set a rule that prevents
, an attribute from being null. A null can create an issue when a function
like average is used.
17.What is a foreign key?: A foreign key is the primary key of one
table that has been placed into another table to create a common
attribute. For instance, a student id number could be the primary key
for information on a student but a foreign key for a table containing
a class roster.
18.What is referential integrity?: Referential integrity is the condition in
which every reference to an entity instance by another entity is valid.
In other words, a foreign key needs to be either null or a valid
primary key in another table.
19.What is a primary key?: A primary key is a candidate key selected to
uniquely identify all other attributes in a given row and it may not
contain null entries. Examples of this include student ID's and social
security numbers.
20.What is a secondary key?: A secondary key is a key that is used
strictly for data retrieval purposes. A secondary key does not always
return a unique outcome. For instance, if a person doesn't know their
student ID, you could still look them up by their first and last name in
the system but that might return several students
1. What is a table?: A table is a persistent representation of a logical
relation that is a relation whose contents can be saved for permanent
use.
2. What are the characteristics of a relational table?: The
characteristics of a relational table are that a table is perceived as a
two-dimensional structure composed of rows and columns, each
row (tuple) represents a single entity
occurrence within the set, each column represents an attribute, each
column has a distinct name, each intersection of a row and column
represents a single data value, all values in a column must be of the
same data format, the order of the rows and columns don't matter to
the DBMS, and
each table must have an attribute (or combination of attributes)
that uniquely identifies each row (tuple).
3. What is a tuple?: A tuple is a row that represents a single entity
occurrence within a set.
4. What are records?: A record is the same as a tuple (row).
5. What is a field?: A field is a column.
6. What is a key?: A key consists of one or more attributes that
determine other attributes. For example, a social security number
identifies all of the other attributes related to that person.
7. What is determination?: Determination is the state in which knowing
,the value of one attribute allows you to determine the value of another
attribute. For example, if you know a key, you can find other
information.
8. What is functional dependence?: Functional dependence is when
knowing the value of one or more attributes lets you know the value of
the other attributes. For example, knowing the first name and the
social security number would let you find the person's last name.
9. What is full functional dependence?: Full functional dependence is
when knowing the value of one or more attributes lets you know the
value of other attributes and the value of the known attributes are
NEEDED to find the other attributes. For example, a social security
number lets you find the first and last name of someone. This is full
functional dependence. If it was a social security number and a first
name this would just be functional dependence because the first
name is not required to look up the last name. All you need is the
SSN.
10.What is a determinant?: A determinant is an attribute whose value
deter- mines the value of other attributes. For example, a social
security number could be the determinant for your last name.
,11.What is a dependent?: A dependent is an attribute whose value is
determined by another attribute. For example, you last name could be
a dependent of your social security number.
12.What is a composite key?: A composite key is a key that is
composed of one or more attribute. For example, the key of your last
name and you social security number could be used to determine your
first name. This would be a composite key because you are using your
last name and your SSN in the key.
13.What is a superkey?: A superkey is a key that can uniquely identify
any row in a table. Some examples of this would be your social
security number identifying a row corresponding to your information,
but a superkey isn't limited to full functional dependence. Your SSN
and your last name used as a key would still be a superkey.
14.What is a candidate key?: A candidate key is a minimal super key.
This is to say it has no extra attributes. If you only need a social
security number to identify the row related to a person than the
candidate key is the SSN. A key consisting of an SSN and the last
name in this case would not be a candidate key.
15.What is entity integrity?: Entity integrity is the condition in which
each row (entity instance or tuple) in the table has it's own unique
identity. This requires that all values in the primary key be unique and
that the primary key cannot be null.
16.What is a null?: A null is the absence of a data value. A null should
be avoided whenever possible. In fact, you can set a rule that prevents
, an attribute from being null. A null can create an issue when a function
like average is used.
17.What is a foreign key?: A foreign key is the primary key of one
table that has been placed into another table to create a common
attribute. For instance, a student id number could be the primary key
for information on a student but a foreign key for a table containing
a class roster.
18.What is referential integrity?: Referential integrity is the condition in
which every reference to an entity instance by another entity is valid.
In other words, a foreign key needs to be either null or a valid
primary key in another table.
19.What is a primary key?: A primary key is a candidate key selected to
uniquely identify all other attributes in a given row and it may not
contain null entries. Examples of this include student ID's and social
security numbers.
20.What is a secondary key?: A secondary key is a key that is used
strictly for data retrieval purposes. A secondary key does not always
return a unique outcome. For instance, if a person doesn't know their
student ID, you could still look them up by their first and last name in
the system but that might return several students
