dbms

🔹 1. Data Modeling & ER Diagrams

Entity: A real-world object we store data about.

Attribute: A property or characteristic of an entity.

Relationship: Logical link between entities.

Keys:

Candidate Key: Any attribute set that could serve as a primary key.

Primary Key: Main key chosen to uniquely identify records.

Alternate Key: Candidate key not chosen as the primary.

Surrogate Key: Artificial key (e.g., auto-increment ID).

Composite Key: A key with more than one attribute.

Foreign Key (FK): Links records between tables.

Cardinality:

Min Cardinality: Minimum participation in a relationship.

Max Cardinality: Maximum participation.

Crow’s Foot Notation: Used to visually represent cardinality.

Special Entities:

Strong Entity: Exists independently with full primary key.

Weak Entity: Depends on strong entity; uses identifying relationship.

🔹 2. Functional Dependency & Normalization

Functional Dependency: A → B means A determines B.

Determinant: Left side of dependency.

Normalization Goals: Reduce redundancy, fix CUD anomalies.

Normal Forms:

1NF: Eliminate repeating groups.

2NF: No partial dependency (only if composite PK).

3NF: No transitive dependency (non-key depends on non-key).

CUD Anomalies:

Insertion: Can't add data due to missing related info.

Update: Inconsistency due to redundancy.

Deletion: Unintentional data loss.

🔹 3. Database Design

Conceptual Model: High-level (entities, relationships).

Logical Model: Schema-level (attributes, FKs).

Physical Model: Implementation-level (data types, constraints).

Data Types (MySQL Examples):

String: VARCHAR, CHAR

Numeric: INT, DECIMAL(8,2)

Date/Time: DATE, DATETIME

Field Constraints:

Default value