diff --git a/packages/okf/src/ossie/detect.ts b/packages/okf/src/ossie/detect.ts
index f96b7fcd..ac7a3d79 100644
--- a/packages/okf/src/ossie/detect.ts
+++ b/packages/okf/src/ossie/detect.ts
@@ -19,7 +19,8 @@ export function detectModelFormat(input: { fileName?: string; text: string }): M
   const first = (lines[i] ?? "").trimStart();
   const looksOssie = first.startsWith("{") || OSSIE_KEY.test(first);
   // Frontmatter in OKF docs can also start with `name:` / `version:`, so also
-  // require a top-level `datasets` / `semantic_model` key.
-  const hasModelKey = /^(datasets|semantic_model)\s*:/m.test(lines.join("\n")) || /"(datasets|semantic_model)"\s*:/.test(text);
+  // require a top-level Ossie key. Ontology and mapping documents count too:
+  // the Ossie reader explains that they aren't semantic models.
+  const hasModelKey = /^(datasets|semantic_model|ontology|concept_mappings)\s*:/m.test(lines.join("\n")) || /"(datasets|semantic_model|ontology|concept_mappings)"\s*:/.test(text);
   return looksOssie && hasModelKey ? "ossie" : "okf";
 }
diff --git a/packages/okf/src/ossie/parse.ts b/packages/okf/src/ossie/parse.ts
index 44c0fdd9..e66ad478 100644
--- a/packages/okf/src/ossie/parse.ts
+++ b/packages/okf/src/ossie/parse.ts
@@ -42,6 +42,23 @@ export function parseOssie(text: string): OssieImport {
   }
 }
 
+const USE_SEMANTIC_MODEL = 'The canvas imports semantic models: import the file with a top-level "datasets" list instead.';
+
+// Ossie also has ontology documents (business concepts) and mapping documents
+// (ontology ↔ semantic model). Neither describes datasets, so say what the file
+// is instead of a bare "not an Ossie model".
+function notSemanticModelMessage(obj: Record<string, unknown>): string {
+  if (Array.isArray(obj.concept_mappings)) {
+    const ref = isObj(obj.semantic_model_ref) ? obj.semantic_model_ref.iri : undefined;
+    const iri = typeof ref === "string" ? ref.trim().slice(0, 200) : "";
+    return iri
+      ? `This is an Apache Ossie mapping document, not a semantic model. Import the semantic model it points to instead: ${iri}`
+      : `This is an Apache Ossie mapping document, not a semantic model. ${USE_SEMANTIC_MODEL}`;
+  }
+  if (Array.isArray(obj.ontology)) return `This is an Apache Ossie ontology (business concepts), not a semantic model. ${USE_SEMANTIC_MODEL}`;
+  return "This file isn't an Ossie model";
+}
+
 function convert(text: string): OssieImport {
   let raw: unknown;
   try { raw = YAML.parse(text, { maxAliasCount: 100 }); }
@@ -60,7 +77,7 @@ function convert(text: string): OssieImport {
   } else if (Array.isArray(obj.datasets)) {
     doc = obj as unknown as OssieDoc;
   } else {
-    throw new Error("This file isn't an Ossie model");
+    throw new Error(notSemanticModelMessage(obj));
   }
 
   const vendors: string[] = [];
diff --git a/packages/okf/test/ossie-detect.test.ts b/packages/okf/test/ossie-detect.test.ts
index 00dc5214..acc14fbf 100644
--- a/packages/okf/test/ossie-detect.test.ts
+++ b/packages/okf/test/ossie-detect.test.ts
@@ -15,4 +15,8 @@ describe("detectModelFormat", () => {
     expect(detectModelFormat({ text: "---\nname: Orders\ntitle: Orders\n---\n# Orders" })).toBe("okf");
     expect(detectModelFormat({ text: "<!-- shop/a.md -->\n---\ntitle: A\n---" })).toBe("okf");
   });
+  it("routes pasted Ossie ontologies and mappings to the Ossie reader (which explains them)", () => {
+    expect(detectModelFormat({ text: "version: 0.2.0.dev0\nname: Flights\nontology:\n- concept: Airport" })).toBe("ossie");
+    expect(detectModelFormat({ text: "version: 0.2.0.dev0\nname: m\nconcept_mappings:\n- concept: Runway" })).toBe("ossie");
+  });
 });
diff --git a/packages/okf/test/ossie-parse.test.ts b/packages/okf/test/ossie-parse.test.ts
index b90f6f31..5b05a706 100644
--- a/packages/okf/test/ossie-parse.test.ts
+++ b/packages/okf/test/ossie-parse.test.ts
@@ -93,3 +93,25 @@ describe("parseOssie — malformed but parseable input", () => {
     expect(r.graph.edges[0].keys).toEqual([{ left: "a", right: "c" }]);
   });
 });
+
+describe("parseOssie — Ossie documents that aren't semantic models", () => {
+  const ontology = "version: 0.2.0.dev0\nname: Flights\nontology:\n- concept: Airport\n  type: EntityType\n";
+  const mapping = "version: 0.2.0.dev0\nname: flights_mapping\nontology_ref:\n  name: Flights\n  iri: ./flights.ontology.yaml\nsemantic_model_ref:\n  name: Flights semantic model\n  iri: ./flights.semantic_model.yaml\nconcept_mappings:\n- concept: Runway\n";
+  it("explains that an ontology isn't a semantic model", () => {
+    expect(() => parseOssie(ontology)).toThrow(/Apache Ossie ontology/);
+    expect(() => parseOssie(ontology)).toThrow(/top-level "datasets" list/);
+  });
+  it("treats the legacy combined file (ontology + ontology_mappings) as an ontology", () => {
+    expect(() => parseOssie(`${ontology}ontology_mappings:\n- name: m\n`)).toThrow(/Apache Ossie ontology/);
+  });
+  it("points a mapping document at the semantic model it references", () => {
+    expect(() => parseOssie(mapping)).toThrow(/Apache Ossie mapping/);
+    expect(() => parseOssie(mapping)).toThrow(/flights\.semantic_model\.yaml/);
+  });
+  it("still explains a mapping without a usable semantic model reference", () => {
+    expect(() => parseOssie("concept_mappings: []\nsemantic_model_ref: 5\n")).toThrow(/Apache Ossie mapping.*top-level "datasets" list/);
+  });
+  it("keeps the generic error for anything else", () => {
+    expect(() => parseOssie("ontology: nope")).toThrow("This file isn't an Ossie model");
+  });
+});
diff --git a/packages/web/public/ossie-format.md b/packages/web/public/ossie-format.md
index 3219128c..865d5ec0 100644
--- a/packages/web/public/ossie-format.md
+++ b/packages/web/public/ossie-format.md
@@ -15,6 +15,8 @@
 
 The canvas reads the flat `0.2.x` document and the legacy `semantic_model: [ ... ]` wrapper (YAML or JSON). With several models in one file, it imports the first and tells you how many it skipped.
 
+**Ontologies and mappings are not imported yet.** Ossie also defines ontology documents (`ontology:` — business concepts, see [ontology.md](https://github.com/apache/ossie/blob/main/ontology/ontology.md)) and mapping documents (`concept_mappings:` — ontology ↔ semantic model). They describe no datasets, so the import dialog says what the file is and asks for the semantic model instead. For a mapping document it names the semantic model the mapping points to (`semantic_model_ref.iri`). In the Ossie examples, `flights.semantic_model.yaml` imports; `flights.ontology.yaml`, `flights.mapping.yaml` and `flights.yaml` do not.
+
 ---
 
 ## What the canvas reads
diff --git a/packages/web/src/okf/io.test.ts b/packages/web/src/okf/io.test.ts
index 0095fc51..671b0069 100644
--- a/packages/web/src/okf/io.test.ts
+++ b/packages/web/src/okf/io.test.ts
@@ -53,6 +53,11 @@ describe("loadModel*", () => {
     await expect(loadModelFiles({ "m.yaml": OSSIE, "a.md": "---\ntitle: A\n---" })).rejects.toThrow("Import one format at a time");
     await expect(loadModelFiles({ "a.json": '{"a":1}' })).rejects.toThrow("This file isn't an Ossie model");
   });
+  it("explains an Ossie ontology from a file or pasted text", async () => {
+    const onto = "version: 0.2.0.dev0\nname: Flights\nontology:\n- concept: Airport\n  type: EntityType\n";
+    await expect(loadModelFiles({ "flights.ontology.yaml": onto })).rejects.toThrow(/Apache Ossie ontology/);
+    await expect(loadModelText(onto)).rejects.toThrow(/Apache Ossie ontology/);
+  });
 });
 
 describe("size cap", () => {