Mock Exam Review - Database Systems

These flashcards cover key concepts and definitions related to the mock exam on Database Systems, enhancing understanding of critical topics.

Relational Calculus

A non-procedural query language used to express queries in relational databases.

Query Optimization

The process of choosing the most efficient query execution plan for a given query.

Extended ER-Diagram

An enhanced version of the Entity-Relationship diagram that includes features like inheritance and categories.

Inheritance in ER-Diagrams

A mechanism where an entity can inherit attributes and relationships from another entity.

ACID Properties

A set of properties that guarantee database transactions are processed reliably: Atomicity, Consistency, Isolation, Durability.

Loss Update Problem

An issue that occurs when multiple transactions update the same data, resulting in lost updates.

Unrepeatable Read

A phenomenon where a transaction reads the same row multiple times and gets different values due to concurrent updates.

Phantom Read

A situation where a transaction reads a set of rows that match a condition, but another transaction inserts or deletes rows that would change the result set.

Two-Phase Locking (2PL)

A concurrency control mechanism that ensures conflicts are avoided by acquiring all necessary locks before releasing any.

Serializability

The property of a schedule that ensures the result is the same as if transactions were executed in some sequential order.

Polymorphism in Databases

A concept in databases where entities can take on multiple forms depending on their context.

Polyinstantiation

A technique in database systems allowing multiple instances of the same data at different security levels.