What is a semantic layer?
A semantic layer is the place the business writes down what its data means, so a dashboard, an analyst or an agent reads the same definition. In the warehouse world that usually means governed metrics over tables. In a knowledge graph it means an ontology plus the graph built from it, written to W3C Semantic Web standards so the model is not bound to one vendor. graph.build is the second kind: definitions you can design, test and govern, and a graph those definitions actually fill.
How is a semantic layer different from a warehouse metrics layer?
A metrics layer describes tables so two dashboards agree about a number. A graph-based semantic layer describes entities and the relationships between them, so a question that crosses systems, such as whether this customer is the account holder in billing, has an answer that is not a join you write each time. They are complementary. If you have a metrics layer, keep it. It will not author an ontology or materialize a knowledge graph, and this platform will not replace it.
What is the difference between a semantic layer and an ontology?
An ontology is the vocabulary: the classes, the properties, the rules. A semantic layer that stops there still needs a second system to become a graph of your records. graph.build treats the ontology as the first half of the layer and the mapping and load as the second, so the picture on the canvas is the thing the Transformers run. The longer explanation of ontologies is the fundamentals guide.
Is graph.build the only dedicated semantic layer that does both?
The combination is rare, and that is the claim: design, test and build, on W3C Semantic Web standards, without binding the model to one graph vendor. Metrics layers do not author ontologies or build a knowledge graph. Ontology platforms do not run the load against your systems. Graph database tooling is built around one store. If you are evaluating one that does all of it, the comparison to make is whether the model is OWL you can take with you and whether the mappings are RML you can read.
Which W3C standards does graph.build follow?
The ontology is OWL and RDFS. The graph is RDF. The mappings are RML and R2RML. Provenance uses W3C PROV. The Writers speak SPARQL, and also openCypher and Gremlin so the same model can land in a property graph store. Those are the standards that make the layer portable. A semantic layer that uses a private format is a layer you rebuild when the vendor changes.
Does platform-agnostic mean we cannot pick a database?
No. You pick one, and you can change it. The Writers speak SPARQL, openCypher and Gremlin, which covers Amazon Neptune, Neo4j, Stardog, Memgraph, GraphDB, RDFox and the rest of the compatibility page. The model does not have to be rewritten when the store does.
Can an agent use this semantic layer?
Yes. The graph is queried in the database you already run, under the access control you already put there. Studio also publishes a read-only MCP server so an assistant can read the ontology itself: the classes, the properties and the relationships, before it asks a question. That is context, not a pile of chunks. The longer version is the Context for AI page.