cmsc424 q1

Cardinality Ratio

Maximum number of entities related:

• One-to-One

• One-to-Many

• Many-to-One

• Many-to-Many

Cardinality Constraint

Specifies optional vs mandatory participation.

Attributes of a Relationship

Properties specific to a relationship (e.g., Date Completed for EMPLOYEE completes COURSE).

Associative Entity

A relationship turned into an entity when it has attributes or independent meaning (e.g., CERTIFICATE for EMPLOYEE–COURSE).

Unary Relationship

Entity related to itself (e.g., EMPLOYEE supervises EMPLOYEE).

Ternary Relationship

 Involves three entities (e.g., SUPPLIER supplies PRODUCT to WAREHOUSE).

EER

Extension of ER with inheritance concepts.

Specialization

Defining sub-sets of a super-entity (e.g., PERSON → EMPLOYEE, STUDENT).

Generalization

Combining multiple entity sets into a higher-level super-entity (e.g., CAR, TRUCK → VEHICLE).

Disjointness

Subsets cannot overlap (e.g., a PERSON is either EMPLOYEE or STUDENT, not both).

Overlap

Subsets can overlap (e.g., a PERSON can be both STUDENT and EMPLOYEE).

Completeness

Every super-entity instance must belong to a subset.

Partial Specialization

Some super-entity instances may not belong to any subset.

Single Inheritance

A subset has one super-set (like Java classes).

Multiple Inheritance

A subset can have multiple super-sets (like C++ classes).

Relational Database

Data represented as tables (relations).

Relation (Table)

2D table of rows and columns.

Tuple (Row)

One record in a relation.

Attribute (Column)

Named property of a relation.

Primary Key

Unique identifier for tuples in a relation (cannot be NULL).

Composite Key

Primary key formed from multiple attributes.

Foreign Key

Attribute in one table referencing a primary key in another.

Domain Constraint

Attribute values must come from a defined domain.

Entity Integrity Constraint

Primary key must be non-null and unique.

Referential Integrity Constraint

Foreign key must match a primary key or be NULL.

Redundancy

Duplicate data in poorly structured relations.

Insertion Anomaly

Cannot add a record without unnecessary NULLs.

Deletion Anomaly

Deleting data unintentionally removes other useful data.

Insertion Anomaly

Multiple updates required to keep data consistent.

Functional Dependency (FD)

Relationship where one attribute determines another.

Closure of FDs (F⁺)

All functional dependencies that can be inferred from a given set.

Closure of Attributes (α⁺)

All attributes functionally determined by a given set under F.

Canonical Cover

Minimal set of dependencies equivalent to the original set, with no extraneous attributes.

Extraneous Attribute

Attribute in an FD that can be removed without changing closure.

Degree of Relationship

Number of participating entity sets (Unary, Binary, Ternary).

Relationship Set

Collection of similar relationships.

Relationship

Association between entities (e.g., INSTRUCTOR advises STUDENT).

Weak Entity Set

Depends on another entity (e.g., DEPENDENT of EMPLOYEE).

Strong Entity Set

Exists independently (e.g., EMPLOYEE).

Domain (Value Set)

Allowed values for an attribute.

Composite Key

Identifier formed by multiple attributes (e.g., building + room_number).

Identifier (Key)

Attribute(s) uniquely identifying an entity (e.g., UID for STUDENT).

Optional Attribute

May be NULL.

Required Attribute

Must have a value.

Derived Attribute

Computed from other attributes (e.g., Age).

Stored Attribute

Directly stored (e.g., Date of Birth).

Multi-valued Attribute

Multiple values possible (e.g., Skills).

Single-valued Attribute

Only one value per entity (e.g., Date of Birth).

Composite Attribute

Can be broken into sub-parts (e.g., Address = Street, City, Zip).

Simple Attribute

Cannot be divided further (e.g., age).

Attribute

Entity Instance

Entity Set

Collection of entities with shared properties (e.g., STUDENT).