Schema.org is technically an ontology, not just a markup language. An ontology in computer science is a formal system that defines a set of concepts, their properties, and how they relate to each other. Schema.org does exactly this using RDF (Resource Description Framework) standards—it specifies that a "Person" can have properties like "name" and "jobTitle," and that an "Organization" can have "employees" who are "Person" entities. This ontological structure is what makes schema markup powerful for SEO. When you add JSON-LD structured data to a page, you're not just tagging content—you're mapping it to a shared conceptual model that Google, Bing, and other engines understand. A product page marked up with Product schema tells search engines "this entity has a price, a brand, and aggregateRating properties" in a way they can parse reliably across millions of sites. The practical distinction matters because ontologies are extensible and hierarchical. Schema.org's types inherit properties from parent classes. A "LocalBusiness" inherits all properties from "Organization," which inherits from "Thing." This cascading structure means you can describe complex entities accurately without reinventing terms. At Ottawa SEO, we treat schema implementation as semantic modeling, not box-checking. For a multi-location client, we might use: - Organization schema at the brand level - LocalBusiness for each location with proper address and geo coordinates - Service schema for individual offerings - BreadcrumbList to clarify site hierarchy The ontological foundation ensures these entities relate correctly. Google's Knowledge Graph ingests this structured data to build entity relationships, which directly impacts visibility in rich results, local packs, and knowledge panels. The mistake most sites make is treating schema as optional metadata. Because it's an ontology, incomplete or contradictory markup confuses parsers. If your Product schema lists a price but your Offer nested inside contradicts it, you've broken the semantic model. Validate everything through Google's Rich Results Test and Schema Markup Validator—ontologies require precision, and search engines penalize logical inconsistencies by ignoring the markup entirely.