CIS 3050 Chapter 4 Terms and Definitions

Relation

A named, two-dimensional table of data.

Primary key

An attribute or a combination of attributes that uniquely identifies each row in a relation.

Composite key

A primary key that consists of more than one attribute.

Foreign key

An attribute in a relation that serves as the primary key of another relation in the same database.

Null

A value that may be assigned to an attribute when no other value applies or when the applicable value is unknown.

Entity integrity rule

A rule that states that no primary key attribute (or component of a primary key attribute) may be null.

Referential integrity constraint

A rule that states that either each foreign key value must match a primary key value in another relation or the foreign key value must be null.

Well-structured relation

A relation that contains minimal redundancy and allows users to insert, modify, and delete the rows in a table without errors or inconsistencies.

Anomaly

An error or inconsistency that may result when a user attempts to update a table that contains redundant data. The three types of anomalies are insertion, deletion, and modification anomalies.

Recursive foreign key

A foreign key in a relation that references the primary key values of the same relation.

Normalization

The process of decomposing relations with anomalies to produce smaller, well-structured relations.

Normal form

A state of a relation that requires that certain rules regarding relationships between attributes (or functional dependencies) are satisfied.

Functional dependency

A constraint between two attributes in which the value of one attribute is determined by the value of another attribute.

Determinant

The attribute on the left side of the arrow in a functional dependency.

Candidate key

An attribute, or combination of attributes, that uniquely identifies a row in a relation.

First normal form (1NF)

A relation that has a primary key and in which there are no repeating groups.

Second normal form (2NF)

A relation in first normal form in which every nonkey attribute is fully functionally dependent on the primary key.

Partial functional dependency

A functional dependency in which one or more nonkey attributes are functionally dependent on part (but not all) of the primary key.

Third normal form (3NF)

A relation that is in second normal form and has no transitive dependencies.

Transitive dependency

A functional dependency between the primary key and one or more nonkey attributes that are dependent on the primary key via another nonkey attribute.

Synonyms

Two (or more) attributes that have different names but the same meaning.

Alias

An alternative name used for an attribute.

Homonym

An attribute that may have more than one meaning.

Enterprise key

A primary key whose value is unique across all relations.

Data integrity

Mechanisms for implementing business rules that maintain integrity of manipulated data

Domain Constraints

Allowable values for an attribute (includes data types and restrictions on values)

Insertion Anomaly

adding new rows forces user to create duplicate data

Deletion Anomaly

deleting rows may cause a loss of data that would be needed for other future rows

Modification Anomaly

changing data in a row forces changes to other rows because of duplication

Surrogate Primary Key

A serial number or other system-assigned primary key for a relation.