MIS 336 test #3
ZIP codes
A classic example of unneeded normalization is when we are dealing with
True
A data model is a plan for a database design
The value is appropriate but unknown
A null value can indicate which of the following conditions
Recrusive
A table is related to itself. Example: organizational chart
Faster querying
An advantage of denormalization
Discriminator
An attribute that determines which subtype should be used is a _________
True
An entity instance is an occurrence of a particular entity
Weak entity
An entity whose identifier includes the identifier of another entity is a _________
True
An identifier of an entity instance is one of more attributes that name or identify entity instance
The supertype
Can only have one subtype
True
In a 1:N relationship, the parent entity is on the one side of the relationship, and the child entity is on the many side of the relationship
Normalization
For a number of reasons, ______ is NOT often an advantage for a read-only database
The supertype
Has all of the common fields
The subtype
Has the fields that are different on the ER diagram there is a circle with a line under it
discriminator
If the circle has an X in it, it means
Solid line
In ER diagrams the relationship line is a ___
Null value
Is a missing value
Strong entity
Is an entity that represents something that can exist on its own
weak entity
Is an entity whose existence depends on the presence of another entity
The inconsistent values problem
Is the same as the problem of misspelled data entries
intersection table
Is two entities are the parent there's a third table. It holds only the primary keys of the two tables as foreign keys. This combination of keys serves as the composite primary key of the intersection table itself. This tables only holds key data
Denormalization
Is used in the data warehouses, data or data mining, or analytics. NO worries about Anamolies
If there's no discriminator
It can be partial or total subtype
True
It's okay to have a table in the parent side that is not in the child side. However, it is NOT okay to have a table in the child side that is not in the parent side
Associative Entity
Similar to many to many but interesection table has another field
Archtype/instance
The child is the physical manifestation of the parent, the child is weak, but not id dependent
True
The degree of a relationship is the number of entity classes in the relationship
More complex SQL for multitable subqueries and joins
The disadvantage of normalization include ____
Denormalization
The process of joining two or more tables and storing the results as a single table
NO X in the circle
The supertype can have no subtypes or many subtypes
ID-dependent entity
The weak entities has the identifier of the parent (solid line )
ID independent (non ID dependent)
The weak entity doesn't nor have the identifier of the parent (dashed line )
Total
There is a line below the supertype, then the supertype has to have one subtype
Partial
There is no extra line below the supertype, then the supertype doesn't have to have a subtype
IS NULL
To check for null values in a column in a table, use the __________ phrase.
To eliminate NULL values
What supertype/subtype are used primarily for ?
Foreign Key
When checking for referential integrity with a subquery, the top level query should always be the table with the ______ key
The missing values problem
When some data values that were provided were never entered into the table. It's an example of _____
All subtypes of a supertype must have the same attributes
Which of the following is NOT true about subtype entities
Subquries and joins
With many tables we have to use ______ and ________
recursive relationship
when an entity is related to itself.