William Kent's Classic Guide to the Five Normal Forms (1982)

William Kent's 1982 paper, later published in Communications of the ACM, remains one of the clearest explanations of relational database normalization ever written. It walks through first through fifth normal forms using plain-language examples rather than dense mathematical notation, showing how each form eliminates specific categories of data redundancy and update anomalies.

The guide's core insight is definitional: a non-key field must depend on the whole key, nothing but the key, and only single-valued facts should coexist in one record. Kent illustrates second and third normal form violations with concrete inventory and employee examples, then extends into functional dependencies and the subtler distinction between single-valued facts and formal functional dependencies — a distinction that matters when identifiers aren't unique.

For engineers, this paper is a foundational text: schema design decisions in SQL databases, many anomaly bugs in production data, and countless 'why is this table structured that way' questions trace back to reasoning first formalized here. Four decades after being written, it remains a common reference in database courses and interview prep for backend and data engineers.