The interviews are done. Someone sat with the domain expert and committed ontology.md next to the code. Then the quarter got busy. Six months later a report counts the same Customer three times, and the model built to prevent exactly that has not changed since launch. An ontology earns its keep only when a team uses it. A software ontology is a shared model of a domain: its entities, their attributes, and their relationships, written so people and code agree on what each term means. This guide assumes the model already exists. The goal is to put it to work: in workflows, design sessions, database schemas, and on every screen where a teammate looks something up. Pick the section that matches the task in front of you. The command examples assume PostgreSQL and psql , but the practice maps to any engine that supports comments and constraints. The examples use the Subscription Billing context from the creation guide , so the terms line up across both articles.