4. Relational Model

Domain

Set of allowable values for an attribute.

Degree

Number of attributes (columns) in a relation.

Cardinality (Relational Table)

Number of tuples (rows) in a relation; different from relationship cardinality.

Relational Table Characteristics

Unique column names, single values per cell, consistent data types, and a unique identifier for each row.

Key

One or more attributes that determine other attributes.

Composite Key

Key consisting of two or more attributes.

Principle of Determination

Knowing attribute A allows you to determine attribute B.

Functional Dependency

When each value of A determines exactly one value of B; written A → B.

Determinant

Attribute on the left side of a functional dependency (A in A → B).

Dependent

Attribute on the right side of a functional dependency (B in A → B).

Superkey

Attribute(s) that uniquely identify each row in a table.

Candidate Key

Minimal superkey; contains no unnecessary attributes.

Primary Key (PK)

Selected candidate key that uniquely identifies each row; cannot be null.

Foreign Key (FK)

Attribute(s) referencing a key in another relation; may be null if permitted.

Secondary Key

Attribute(s) used strictly for data retrieval.

Entity Integrity

Primary key values must be unique and cannot be null.

Referential Integrity

Foreign key must match a referenced key or be null if allowed.

General Constraints

Additional restrictions based on business rules to maintain data integrity.

NO ACTION

Rejects deletion of a parent row if dependent child rows exist.

CASCADE

Updates or deletes matching child rows when the parent row is updated or deleted.

SET NULL

Sets child foreign keys to null when the parent is deleted; requires nullable foreign keys.

SET DEFAULT

Sets child foreign keys to a specified default value when the parent is deleted.

Parent Relation

Table containing the key referenced by a foreign key in another table.

Child Relation

Table containing the foreign key referencing the parent relation.

NOT NULL Constraint

Requires every row to have a value for the specified attribute.

UNIQUE Constraint

Prevents duplicate values in a specified attribute.

Flags (Dummy Values)

Fake placeholder values used instead of nulls; should be avoided for legitimately unknown data.

Historical Data Redundancy

Intentional duplication of data to preserve historical accuracy, such as an invoice's original price.

Relational Schema

Relation name followed by attributes in parentheses; PK bold and underlined, FK italicized.

Relational Database Schema

Collection of all relation schemas in a database.

1:M Relationship in Relational Model

Preferred relationship type; one parent row may relate to many child rows.

1:1 Relationship in Relational Model

One row relates to one other row; sometimes suggests entities could be combined.

M:N Relationship Resolution

Create a composite entity to convert M:N into two 1:M relationships.

Composite Entity

Bridge table containing foreign keys referencing the two related entities.

Homonym

Same attribute name used for different meanings; should be avoided.

Synonym

Different attribute names used for the same meaning; should be avoided.

Relational Model Documentation

Identifies keys, relationships, business rules, and actions when records are updated or deleted.