- Note of CMU Course 15-445/645 Database Systems, including data models (relational, document, key/value), storage models (n-ary, decomposition), storage architectures (heaps, log-structured), indexing (order preserving trees, hash tables), transaction processing (ACID, concurrency control), recovery (logging, checkpoints), query processing (joins, sorting, aggregation, optimization), and parallel architectures (multi-core, distributed).