WGU C170 Data Management Applications (over 200 Questions & Answers)
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WGU C170
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WGU C170
WGU C170 Data Management Applications (over 200 Questions & Answers)
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.
What are the characteristics of a relational table?
The characteristics of a rel...
WGU C170 Data Management Applications (over 200
Questions & Answers)
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.
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).
What is a tuple?
A tuple is a row that represents a single entity occurrence within a set.
What are records?
A record is the same as a tuple (row).
What is a field?
A field is a column.
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.
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.
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.
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.
What is a determinant?
A determinant is an attribute whose value determines the value of other attributes. For
example, a social security number could be the determinant for your last name.
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.
,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.
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.
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.
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.
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.
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.
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.
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.
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 with the same name and you'd have to look
through the list to find the appropriate one.
What is a flag?
A flag is used to indicate the absence of some value to avoid using a null.
What is relational algebra?
Relational algebra defines the theoretical way of manipulating table contents using
relational operators.
, What is a relvar?
A relvar is the variable that holds a relation. It is composed of two parts: a relvar
heading and a relvar body.
What is a relvar heading?
The relvar heading contains the name of the attributes.
What is a relvar body?
A relvar body contains the relation.
What is a relation (not in general terms where you can use table and relation
interchangeably)?
A relation is the data that we see in our tables not the data itself. It's a relationship
between sets of information.
What is the property of closure?
Closure is a property that permits the use of relational operators on existing relations to
create new relations.
What is a unary operator?
A unary operator in regards to SQL is an operator that works on only one table.
What is the SELECT (sometimes referred to as RESTRICT) operator used for?
The SELECT (or RESTRICT) operator is used to select certain rows (aka tuples). It
yields values for all rows that satisfy a given condition. For example a SELECT
statement that looks for students with a gpa below 2.0 could be used to produce a table
with all rows that contain a gpa lower than 2.0. Formally, SELECT is denoted by a lower
case sigma symbol. This is a unary operator that is it only accepts one table as input.
What is the PROJECT operator used for?
The PROJECT operator is a unary operator that will return only the attributes requested
that is to say it yields columns. It does not limit the rows returned so it will return all rows
within the requested columns. Formally it is denoted by the Greek letter pi.
What is the UNION operator?
The UNION operator combines all rows from two tables excluding duplicate rows. To be
used in the UNION the two tables must contain the same attributes. Union is denoted by
a symbol that looks like an uppercase U.
What does it mean to be union-compatible?
Union-compatible means that two or more tables contain the same number of columns
of the same type.
What is an INTERSECTION operator?
An INTERSECTION operator is an operator that yields only rows that are in both tables.
This operator requires that the tables be union-compatible. The symbol for this
operation is similar to an upside down U.
What is the DIFFERENCE operator?
The DIFFERENCE operator is an operator that yields all the rows in one table that are
not found in another table. It is seen as subtraction and it denoted by the minus sign -.
It's important to note that given tables A and B the DIFFERENCE between A and B is
not the same as the DIFFERENCE between B and A. Oder matters.
What is the PRODUCT operator?
The PRODUCT operator is an operator the yields the Cartesian product of two tables
that is it yields all possible pairs of rows of the two tables. So, if one table has 3 rows
and another table has 6 rows the PRODUCT of these two tables will result in a table
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