Chapter 2 Quiz

Domain integrity

Domain integrity uses data types and value constraints to insure valid values are entered for every cell in a column.

Cascade option

The cascade option causes the deletion or update on the one side to cascade into the rows on the many side.

entity class

The collection of all entity instances is called an entity class

Foreign key

A foreign key is a column or columns in one table that are a primary key (or part of a primary key) in a table. Usually the foreign key exists as a primary key in a different table, but it could be the same table. Foreign keys are used to establish relationships between tables and it is the implementation of these relationships that allow relational databases to achieve a high level of data integration with minimal data redundancy.

unary relationship

A unary relationship is when you implement a relationship between a table and itself.

value constraint

A value constraint is an edit that limits (or constrains) the specific value(s) that can be used to a valid range. In the hire date example, the value constraints would be set such that any date values entered would need to be: equal to or greater than the date the company opened for business, and less than or equal to the current date.

Entity instance

An individual entity

Entity integrity

Entity integrity ensures the primary key value for each row is unique and not null.

Declarative language

SQL is a declarative language meaning database users indicate what data is stored in the database and what data needs to be retrieved but the database system handles all the technical details of how the data is stored and retrieved. In other words, users specify the what but not the how.

No action cascade option

The No Action option is a more complicated version of Restrict although in some databases (like MySQL) the two are the same. Both Restrict and No Action cause updates and deletes to fail if there are related rows due to referential integrity. The main difference between Restrict and No Action is when the failure occurs. The Restrict option checks for a related row immediately while No Action checks at the end of the statement. In many cases this difference is irrelevant. For this course just remember there can be differences between the two.

Relation

The basis for storage in a relational database system. The term "table" is often used in place of relation, but a relation has the following characteristics which differentiates it from a table like you might find in a spreadsheet application.

Primary key

The primary key attribute (column) uniquely identifies each tuple (row). The value of the primary key is different for each row and cannot be null (empty).

restrict cascade option

The restrict option is usually the default. That is, it is the one used if no other option is selected. Under this option, deleting a row on the one side of a one-to-many relationship will fail if the deletion would cause a related row to lose its referential integrity. The same applies to updates to rows on the one side of a one-to-many relationship.

referential integrity

insures that a value contained in a foreign key column must match a value stored in the primary key column it "references".