Midterm Flashcards
(15 cards)
How does a deletion anomaly occur?
the unintended loss of data due to deletion of other data
How does an insertion anomaly occur?
The inability to add data to the database due to absence of other data
How does a modification anomaly occur?
unexpected side effect from trying to insert, update, or delete a row
Define a database
A self-describing collection of related records or, for relational databases, of related tables.
What is a foreign key?
Attribute that points to a primary key
What is the purpose of metadata within a database?
Data that is about the data.
example: description of an attribute
In order to implement a many-to-many relationship within a database, what type of entity needs to be placed between the entities that form the many-to-many relationship?
associative entity
What type of relationship is formed when an associative entity is placed between it?
many-to-many relationship
Describe a non-ID dependent weak entity
A weak entity is an entity that cannot exist by itself and a non-ID dependent entity is when a foreign key is not part of a primary key
(essn, pno) -> hours
essn and pno are the determinant
What is the purpose of a primary key?
To identify a row in a table
what is a transitive dependency?
a non-prime attribute that points to another non-prime attribute
3NF has to have ______
2 non-prime attributes
What is a composite key?
Two primary keys
Purpose of a referential integrity constraint
To insure that a foreign key points to a primary key
