Relational model

Data as tables of rows and columns, with no other structure implied.

Also known as: relations, tuples and attributes, relational data model.

Leads to

Entity-relationship modeling: Sketching entities and their relationships as a diagram before turning them into tables.
SQL filtering and projection: Picking which rows and columns you want back with SELECT and WHERE.
Relational algebra: The formal, math-like operations SQL actually compiles down to under the hood.
Functional dependencies: One column's value fully determines another's, e.g. knowing the ID tells you the name.
Storage and file organization: How rows actually get laid out into pages and files on disk.
Transactions and ACID properties: The four guarantees (atomicity, consistency, isolation, durability) that make a transaction feel like one indivisible unit.
NoSQL data models: Alternatives to tables: documents, key-value pairs, wide columns, or graphs, each suited to a different access pattern.