It covers logic and proof, sets and functions, relations, number theory, counting and combinatorics, recurrences, graphs, trees, networks, boolean algebra and automata. The standard syllabus of a first course, with many worked examples and pseudocode.
What I took from it
The chapter on relations, which is literally where the relational model comes from. The properties of a relation — whether an element relates to itself, whether it holds in both directions, whether chaining two implies a third — stop being abstractions the moment you model customer hierarchies, product structures or approval routes. That is where it gets decided whether a query can be written plainly or has to walk a tree by hand.
The counting chapter left me a reflex that has saved me work: when somebody asks for every combination of something, count them first. Four attributes with ten values each is already ten thousand variants, and the conversation changes completely — it stops being a programming problem and becomes a business decision about which combinations actually sell. That arithmetic takes a minute and prevents configurations nobody can maintain.
Recurrences, finally, are what let you reason about processes that call themselves, which show up in an ERP more than people expect: bill of materials explosions, accounting hierarchies, consolidations.
What I left out
Automata, boolean circuits and most of the proofs. And a warning about the book as an object: it is a course text, and the real content is in the exercises. Anyone reading it like an essay will turn the pages with a feeling of understanding and take away almost nothing. That is not the author's fault, it is the genre.