Databases (DBMS)

The Entity-Relationship model is a conceptual design tool; the relational model implements it as tables. GATE tests ER-to-relational mapping, keys, constraints, and schema design.

Relational algebra is the formal query language for relational databases. SQL is the practical implementation. GATE tests RA expressions, SQL queries with JOINs, GROUP BY, and nested queries.

Normalisation removes redundancy and update anomalies from relational schemas using functional dependencies. GATE tests FD closure, canonical cover, and decomposition into BCNF/3NF.

Transactions ensure database consistency under concurrent access. GATE tests ACID properties, serializability, conflict serializability, and lock-based protocols including 2PL.

Indexes speed up data retrieval. B+ trees are the dominant index structure. GATE tests B+ tree operations, dense vs sparse indexes, hashing, and query cost estimation.