Databases

Relational, document, graph models; schema-on-read vs write; SQL, Cypher, SPARQL, Datalog query languages

JSON/XML, Thrift, Protobuf, Avro; schema evolution; forward/backward compatibility; dataflow modes

O/R mapping architectural patterns (Table Data Gateway, Row Data Gateway, Active Record, Data Mapper); behavioural patterns (Unit of Work, Identity Map, Lazy Load); structural mapping; inheritance strategies (Single/Class/Concrete Table Inheritance)

Hash indexes, SSTables/LSM-Trees, B-Trees, OLTP vs OLAP, column-oriented storage, materialized aggregates

ACID, isolation levels (dirty reads, read skew, write skew, phantoms), MVCC, SSI, actual serial execution, 2PL