Import Solver + neighbors via sparql query

.gitignore

@@ -1,2 +1,9 @@
 .direnv/
 .envrc
+.env
+backend/.env
+frontend/node_modules/
+frontend/dist/
+.npm/
+.vite/
+data/

backend/Dockerfile

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+FROM python:3.12-slim
+
+WORKDIR /app
+
+ENV PYTHONDONTWRITEBYTECODE=1 \
+    PYTHONUNBUFFERED=1
+
+COPY requirements.txt /app/requirements.txt
+RUN pip install --no-cache-dir -r /app/requirements.txt
+
+COPY app /app/app
+
+EXPOSE 8000
+
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]
+

backend/app/README.md

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+# Backend App (`backend/app`)
+
+This folder contains the FastAPI backend for `visualizador_instanciados`.
+
+The backend can execute SPARQL queries in two interchangeable ways:
+
+1. **`GRAPH_BACKEND=rdflib`**: parse a Turtle file into an in-memory RDFLib `Graph` and run SPARQL queries locally.
+2. **`GRAPH_BACKEND=anzograph`**: run SPARQL queries against an AnzoGraph SPARQL endpoint over HTTP (optionally `LOAD` a TTL on startup).
+
+Callers (frontend or other clients) interact with a single API surface (`/api/*`) and do not need to know which backend is configured.
+
+## Files
+
+- `main.py`
+  - FastAPI app setup, startup/shutdown (`lifespan`), and HTTP endpoints.
+- `settings.py`
+  - Env-driven configuration (`pydantic-settings`).
+- `sparql_engine.py`
+  - Backend-agnostic SPARQL execution layer:
+    - `RdflibEngine`: `Graph.query(...)` + SPARQL JSON serialization.
+    - `AnzoGraphEngine`: HTTP POST to `/sparql` with Basic auth + readiness gate.
+  - `create_sparql_engine(settings)` chooses the engine based on `GRAPH_BACKEND`.
+- `graph_export.py`
+  - Shared helpers to:
+    - build the snapshot SPARQL query used for edge retrieval
+    - map SPARQL JSON bindings to `{nodes, edges}`.
+- `models.py`
+  - Pydantic response/request models:
+    - `Node`, `Edge`, `GraphResponse`, `StatsResponse`, etc.
+- `rdf_store.py`
+  - A local parsed representation (dense IDs + neighbor-ish data) built only in `GRAPH_BACKEND=rdflib`.
+  - Used by `/api/nodes`, `/api/edges`, and `rdflib`-mode `/api/stats`.
+- `pipelines/graph_snapshot.py`
+  - Pipeline used by `/api/graph` to return a `{nodes, edges}` snapshot via SPARQL (works for both RDFLib and AnzoGraph).
+- `pipelines/layout_dag_radial.py`
+  - DAG layout helpers used by `pipelines/graph_snapshot.py`:
+    - cycle detection
+    - level-synchronous Kahn layering
+    - radial (ring-per-layer) positioning.
+- `pipelines/snapshot_service.py`
+  - Snapshot cache layer used by `/api/graph` and `/api/stats` so the backend doesn't run expensive SPARQL twice.
+- `pipelines/subclass_labels.py`
+  - Pipeline to extract `rdfs:subClassOf` entities and aligned `rdfs:label` list.
+
+## Runtime Flow
+
+On startup (FastAPI lifespan):
+
+1. `create_sparql_engine(settings)` selects and starts a SPARQL engine.
+2. The engine is stored at `app.state.sparql`.
+3. If `GRAPH_BACKEND=rdflib`, `RDFStore` is also built from the already-loaded RDFLib graph and stored at `app.state.store`.
+
+On shutdown:
+
+- `app.state.sparql.shutdown()` is called to close the HTTP client (AnzoGraph mode) or no-op (RDFLib mode).
+
+## Environment Variables
+
+Most configuration is intended to be provided via container environment variables (see repo root `.env` and `docker-compose.yml`).
+
+Core:
+
+- `GRAPH_BACKEND`: `rdflib` or `anzograph`
+- `INCLUDE_BNODES`: `true`/`false`
+- `CORS_ORIGINS`: comma-separated list or `*`
+
+RDFLib mode:
+
+- `TTL_PATH`: path inside the backend container to a `.ttl` file (example: `/data/o3po.ttl`)
+- `MAX_TRIPLES`: optional int; if set, stops parsing after this many triples
+
+Optional import-combining step (runs before the SPARQL engine starts):
+
+- `COMBINE_OWL_IMPORTS_ON_START`: `true` to recursively load `TTL_PATH` (or `COMBINE_ENTRY_LOCATION`) plus `owl:imports` and write a combined TTL file.
+- `COMBINE_ENTRY_LOCATION`: optional override for the entry file/URL to load (defaults to `TTL_PATH`)
+- `COMBINE_OUTPUT_LOCATION`: optional explicit output path (defaults to `${dirname(entry)}/${COMBINE_OUTPUT_NAME}`)
+- `COMBINE_OUTPUT_NAME`: output filename when `COMBINE_OUTPUT_LOCATION` is not set (default: `combined_ontology.ttl`)
+- `COMBINE_FORCE`: `true` to rebuild even if the output file already exists
+
+AnzoGraph mode:
+
+- `SPARQL_HOST`: base host (example: `http://anzograph:8080`)
+- `SPARQL_ENDPOINT`: optional full endpoint; if set, overrides `${SPARQL_HOST}/sparql`
+- `SPARQL_USER`, `SPARQL_PASS`: Basic auth credentials
+- `SPARQL_DATA_FILE`: file URI as seen by the **AnzoGraph container** (example: `file:///opt/shared-files/o3po.ttl`)
+- `SPARQL_GRAPH_IRI`: optional graph IRI for `LOAD ... INTO GRAPH <...>`
+- `SPARQL_LOAD_ON_START`: `true` to execute `LOAD <SPARQL_DATA_FILE>` during startup
+- `SPARQL_CLEAR_ON_START`: `true` to execute `CLEAR ALL` during startup (dangerous)
+- `SPARQL_TIMEOUT_S`: request timeout for normal SPARQL requests
+- `SPARQL_READY_RETRIES`, `SPARQL_READY_DELAY_S`, `SPARQL_READY_TIMEOUT_S`: readiness gate parameters
+
+## AnzoGraph Readiness Gate
+
+`AnzoGraphEngine` does not assume "container started" means "SPARQL works".
+It waits for a smoke-test POST:
+
+- Method: `POST ${SPARQL_ENDPOINT}`
+- Headers:
+  - `Content-Type: application/x-www-form-urlencoded`
+  - `Accept: application/sparql-results+json`
+  - `Authorization: Basic ...` (if configured)
+- Body: `query=ASK WHERE { ?s ?p ?o }`
+- Success condition: HTTP 2xx and response parses as JSON
+
+This matches the behavior described in `docs/anzograph-readiness-julia.md`.
+
+## API Endpoints
+
+- `GET /api/health`
+  - Returns `{ "status": "ok" }`.
+- `GET /api/stats`
+  - Returns counts for the same snapshot used by `/api/graph` (via the snapshot cache).
+- `POST /api/sparql`
+  - Body: `{ "query": "<SPARQL SELECT/ASK>" }`
+  - Returns SPARQL JSON results as-is.
+  - Notes:
+    - This endpoint is intended for **SELECT/ASK returning SPARQL-JSON**.
+    - SPARQL UPDATE is not exposed here (AnzoGraph `LOAD`/`CLEAR` are handled internally during startup).
+- `GET /api/graph?node_limit=...&edge_limit=...`
+  - Returns a graph snapshot as `{ nodes: [...], edges: [...] }`.
+  - Implemented as a SPARQL edge query + mapping in `pipelines/graph_snapshot.py`.
+- `GET /api/nodes`, `GET /api/edges`
+  - Only available in `GRAPH_BACKEND=rdflib` (these use `RDFStore`'s dense ID tables).
+
+## Data Contract
+
+### Node
+
+Returned in `nodes[]` (dense IDs; suitable for indexing in typed arrays):
+
+```json
+{
+  "id": 0,
+  "termType": "uri",
+  "iri": "http://example.org/Thing",
+  "label": null,
+  "x": 0.0,
+  "y": 0.0
+}
+```
+
+- `id`: integer dense node ID used in edges
+- `termType`: `"uri"` or `"bnode"`
+- `iri`: URI string; blank nodes are normalized to `_:<id>`
+- `label`: `rdfs:label` when available (best-effort; prefers English)
+- `x`/`y`: world-space coordinates for rendering (currently a radial layered layout derived from `rdfs:subClassOf`)
+
+### Edge
+
+Returned in `edges[]`:
+
+```json
+{
+  "source": 0,
+  "target": 12,
+  "predicate": "http://www.w3.org/2000/01/rdf-schema#subClassOf"
+}
+```
+
+- `source`/`target`: dense node IDs (indexes into `nodes[]`)
+- `predicate`: predicate IRI string
+
+## Snapshot Query (`/api/graph`)
+
+`/api/graph` currently uses a SPARQL query that returns only `rdfs:subClassOf` edges:
+
+- selects bindings as `?s ?p ?o` (with `?p` bound to `rdfs:subClassOf`)
+- excludes literal objects (`FILTER(!isLiteral(?o))`) for safety
+- optionally excludes blank nodes (unless `INCLUDE_BNODES=true`)
+- applies `LIMIT edge_limit`
+
+The result bindings are mapped to dense node IDs (first-seen order) and returned to the caller.
+
+`/api/graph` also returns `meta` with snapshot counts and engine info so the frontend doesn't need to call `/api/stats`.
+
+If a cycle is detected in the returned `rdfs:subClassOf` snapshot, `/api/graph` returns HTTP 422 (layout requires a DAG).
+
+## Pipelines
+
+### `pipelines/graph_snapshot.py`
+
+`fetch_graph_snapshot(...)` is the main "export graph" pipeline used by `/api/graph`.
+
+### `pipelines/subclass_labels.py`
+
+`extract_subclass_entities_and_labels(...)`:
+
+1. Queries all `rdfs:subClassOf` triples.
+2. Builds a unique set of subjects+objects, then converts it to a deterministic list.
+3. Queries `rdfs:label` for those entities and returns aligned lists:
+   - `entities[i]` corresponds to `labels[i]`.
+
+## Notes / Tradeoffs
+
+- `/api/graph` returns only nodes that appear in the returned edge result set. Nodes not referenced by those edges will not be present.
+- RDFLib and AnzoGraph may differ in supported SPARQL features (vendor extensions, inference, performance), but the API surface is the same.
+- `rdf_store.py` is currently only needed for `/api/nodes`, `/api/edges`, and rdflib-mode `/api/stats`. If you don't use those endpoints, it can be removed later.

backend/app/__init__.py

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+

backend/app/graph_export.py

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+from __future__ import annotations
+
+from typing import Any
+
+
+def edge_retrieval_query(*, edge_limit: int, include_bnodes: bool) -> str:
+    bnode_filter = "" if include_bnodes else "FILTER(!isBlank(?s) && !isBlank(?o))"
+    
+    return f"""
+PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
+PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
+PREFIX owl: <http://www.w3.org/2002/07/owl#>
+
+SELECT ?s ?p ?o
+WHERE {{
+  {{
+    VALUES ?p {{ rdf:type }}
+    ?s ?p ?o .
+    ?o rdf:type owl:Class .
+  }}
+  UNION
+  {{
+    VALUES ?p {{ rdfs:subClassOf }}
+    ?s ?p ?o .
+  }}
+  FILTER(!isLiteral(?o))
+  {bnode_filter}
+}}
+LIMIT {edge_limit}
+"""
+
+
+def graph_from_sparql_bindings(
+    bindings: list[dict[str, Any]],
+    *,
+    node_limit: int,
+    include_bnodes: bool,
+) -> tuple[list[dict[str, object]], list[dict[str, object]]]:
+    """
+    Convert SPARQL JSON results bindings into:
+      nodes: [{id, termType, iri, label}]
+      edges: [{source, target, predicate}]
+
+    IDs are assigned densely (0..N-1) based on first occurrence in bindings.
+    """
+
+    node_id_by_key: dict[tuple[str, str], int] = {}
+    node_meta: list[tuple[str, str]] = []  # (termType, iri)
+    out_edges: list[dict[str, object]] = []
+
+    def term_to_key_and_iri(term: dict[str, Any]) -> tuple[tuple[str, str], tuple[str, str]] | None:
+        t = term.get("type")
+        v = term.get("value")
+        if not t or v is None:
+            return None
+        if t == "literal":
+            return None
+        if t == "bnode":
+            if not include_bnodes:
+                return None
+            # SPARQL JSON uses bnode identifiers without the "_:" prefix; we normalize to "_:id".
+            return (("bnode", str(v)), ("bnode", f"_:{v}"))
+        # Default to "uri".
+        return (("uri", str(v)), ("uri", str(v)))
+
+    def get_or_add(term: dict[str, Any]) -> int | None:
+        out = term_to_key_and_iri(term)
+        if out is None:
+            return None
+        key, meta = out
+        existing = node_id_by_key.get(key)
+        if existing is not None:
+            return existing
+        if len(node_meta) >= node_limit:
+            return None
+        nid = len(node_meta)
+        node_id_by_key[key] = nid
+        node_meta.append(meta)
+        return nid
+
+    for b in bindings:
+        s_term = b.get("s") or {}
+        o_term = b.get("o") or {}
+        p_term = b.get("p") or {}
+
+        sid = get_or_add(s_term)
+        oid = get_or_add(o_term)
+        if sid is None or oid is None:
+            continue
+
+        pred = p_term.get("value")
+        if not pred:
+            continue
+
+        out_edges.append({"source": sid, "target": oid, "predicate": str(pred)})
+
+    out_nodes = [
+        {"id": i, "termType": term_type, "iri": iri, "label": None}
+        for i, (term_type, iri) in enumerate(node_meta)
+    ]
+
+    return out_nodes, out_edges

backend/app/main.py

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+from __future__ import annotations
+
+from contextlib import asynccontextmanager
+import logging
+import asyncio
+
+from fastapi import FastAPI, HTTPException, Query
+from fastapi.middleware.cors import CORSMiddleware
+
+from .models import (
+    EdgesResponse,
+    GraphResponse,
+    NeighborsRequest,
+    NeighborsResponse,
+    NodesResponse,
+    SparqlQueryRequest,
+    StatsResponse,
+)
+from .pipelines.layout_dag_radial import CycleError
+from .pipelines.owl_imports_combiner import (
+    build_combined_graph,
+    output_location_to_path,
+    resolve_output_location,
+    serialize_graph_to_ttl,
+)
+from .pipelines.selection_neighbors import fetch_neighbor_ids_for_selection
+from .pipelines.snapshot_service import GraphSnapshotService
+from .rdf_store import RDFStore
+from .sparql_engine import RdflibEngine, SparqlEngine, create_sparql_engine
+from .settings import Settings
+
+
+settings = Settings()
+logger = logging.getLogger(__name__)
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    rdflib_preloaded_graph = None
+
+    if settings.combine_owl_imports_on_start:
+        entry_location = settings.combine_entry_location or settings.ttl_path
+        output_location = resolve_output_location(
+            entry_location,
+            output_location=settings.combine_output_location,
+            output_name=settings.combine_output_name,
+        )
+
+        output_path = output_location_to_path(output_location)
+        if output_path.exists() and not settings.combine_force:
+            logger.info("Skipping combine step (output exists): %s", output_location)
+        else:
+            rdflib_preloaded_graph = await asyncio.to_thread(build_combined_graph, entry_location)
+            logger.info("Finished combining imports; serializing to: %s", output_location)
+            await asyncio.to_thread(serialize_graph_to_ttl, rdflib_preloaded_graph, output_location)
+
+        if settings.graph_backend == "rdflib":
+            settings.ttl_path = str(output_path)
+
+    sparql: SparqlEngine = create_sparql_engine(settings, rdflib_graph=rdflib_preloaded_graph)
+    await sparql.startup()
+    app.state.sparql = sparql
+    app.state.snapshot_service = GraphSnapshotService(sparql=sparql, settings=settings)
+
+    # Only build node/edge tables when running in rdflib mode.
+    if settings.graph_backend == "rdflib":
+        assert isinstance(sparql, RdflibEngine)
+        if sparql.graph is None:
+            raise RuntimeError("rdflib graph failed to load")
+
+        store = RDFStore(
+            ttl_path=settings.ttl_path,
+            include_bnodes=settings.include_bnodes,
+            max_triples=settings.max_triples,
+        )
+        store.load(sparql.graph)
+        app.state.store = store
+
+    yield
+
+    await sparql.shutdown()
+
+
+app = FastAPI(title="visualizador_instanciados backend", lifespan=lifespan)
+
+cors_origins = settings.cors_origin_list()
+app.add_middleware(
+    CORSMiddleware,
+    allow_origins=cors_origins,
+    allow_credentials=False,
+    allow_methods=["*"],
+    allow_headers=["*"],
+)
+
+
+@app.get("/api/health")
+def health() -> dict[str, str]:
+    return {"status": "ok"}
+
+
+@app.get("/api/stats", response_model=StatsResponse)
+async def stats() -> StatsResponse:
+    # Stats reflect exactly what we send to the frontend (/api/graph), not global graph size.
+    svc: GraphSnapshotService = app.state.snapshot_service
+    try:
+        snap = await svc.get(node_limit=50_000, edge_limit=100_000)
+    except CycleError as e:
+        raise HTTPException(status_code=422, detail=str(e)) from None
+    meta = snap.meta
+    return StatsResponse(
+        backend=meta.backend if meta else app.state.sparql.name,
+        ttl_path=meta.ttl_path if meta and meta.ttl_path else settings.ttl_path,
+        sparql_endpoint=meta.sparql_endpoint if meta else None,
+        parsed_triples=len(snap.edges),
+        nodes=len(snap.nodes),
+        edges=len(snap.edges),
+    )
+
+
+@app.post("/api/sparql")
+async def sparql_query(req: SparqlQueryRequest) -> dict:
+    sparql: SparqlEngine = app.state.sparql
+    data = await sparql.query_json(req.query)
+    return data
+
+
+@app.post("/api/neighbors", response_model=NeighborsResponse)
+async def neighbors(req: NeighborsRequest) -> NeighborsResponse:
+    svc: GraphSnapshotService = app.state.snapshot_service
+    snap = await svc.get(node_limit=req.node_limit, edge_limit=req.edge_limit)
+    sparql: SparqlEngine = app.state.sparql
+    neighbor_ids = await fetch_neighbor_ids_for_selection(
+        sparql,
+        snapshot=snap,
+        selected_ids=req.selected_ids,
+        include_bnodes=settings.include_bnodes,
+    )
+    return NeighborsResponse(selected_ids=req.selected_ids, neighbor_ids=neighbor_ids)
+
+
+@app.get("/api/nodes", response_model=NodesResponse)
+def nodes(
+    limit: int = Query(default=10_000, ge=1, le=200_000),
+    offset: int = Query(default=0, ge=0),
+) -> NodesResponse:
+    if settings.graph_backend != "rdflib":
+        raise HTTPException(status_code=501, detail="GET /api/nodes is only supported in GRAPH_BACKEND=rdflib mode")
+    store: RDFStore = app.state.store
+    return NodesResponse(total=store.node_count, nodes=store.node_slice(offset=offset, limit=limit))
+
+
+@app.get("/api/edges", response_model=EdgesResponse)
+def edges(
+    limit: int = Query(default=50_000, ge=1, le=500_000),
+    offset: int = Query(default=0, ge=0),
+) -> EdgesResponse:
+    if settings.graph_backend != "rdflib":
+        raise HTTPException(status_code=501, detail="GET /api/edges is only supported in GRAPH_BACKEND=rdflib mode")
+    store: RDFStore = app.state.store
+    return EdgesResponse(total=store.edge_count, edges=store.edge_slice(offset=offset, limit=limit))
+
+
+@app.get("/api/graph", response_model=GraphResponse)
+async def graph(
+    node_limit: int = Query(default=50_000, ge=1, le=200_000),
+    edge_limit: int = Query(default=100_000, ge=1, le=500_000),
+) -> GraphResponse:
+    svc: GraphSnapshotService = app.state.snapshot_service
+    try:
+        return await svc.get(node_limit=node_limit, edge_limit=edge_limit)
+    except CycleError as e:
+        raise HTTPException(status_code=422, detail=str(e)) from None

backend/app/models.py

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+from __future__ import annotations
+
+from pydantic import BaseModel
+
+
+class Node(BaseModel):
+    id: int
+    termType: str  # "uri" | "bnode"
+    iri: str
+    label: str | None = None
+    # Optional because /api/nodes (RDFStore) doesn't currently provide positions.
+    x: float | None = None
+    y: float | None = None
+
+
+class Edge(BaseModel):
+    source: int
+    target: int
+    predicate: str
+
+
+class StatsResponse(BaseModel):
+    backend: str
+    ttl_path: str
+    sparql_endpoint: str | None = None
+    parsed_triples: int
+    nodes: int
+    edges: int
+
+
+class NodesResponse(BaseModel):
+    total: int
+    nodes: list[Node]
+
+
+class EdgesResponse(BaseModel):
+    total: int
+    edges: list[Edge]
+
+
+class GraphResponse(BaseModel):
+    class Meta(BaseModel):
+        backend: str
+        ttl_path: str | None = None
+        sparql_endpoint: str | None = None
+        include_bnodes: bool
+        node_limit: int
+        edge_limit: int
+        nodes: int
+        edges: int
+
+    nodes: list[Node]
+    edges: list[Edge]
+    meta: Meta | None = None
+
+
+class SparqlQueryRequest(BaseModel):
+    query: str
+
+
+class NeighborsRequest(BaseModel):
+    selected_ids: list[int]
+    node_limit: int = 50_000
+    edge_limit: int = 100_000
+
+
+class NeighborsResponse(BaseModel):
+    selected_ids: list[int]
+    neighbor_ids: list[int]

backend/app/pipelines/__init__.py

@@ -0,0 +1 @@
+

backend/app/pipelines/graph_snapshot.py

@@ -0,0 +1,148 @@
+from __future__ import annotations
+
+from typing import Any
+
+from ..graph_export import edge_retrieval_query, graph_from_sparql_bindings
+from ..models import GraphResponse
+from ..sparql_engine import SparqlEngine
+from ..settings import Settings
+from .layout_dag_radial import CycleError, level_synchronous_kahn_layers, radial_positions_from_layers
+
+
+RDFS_LABEL = "http://www.w3.org/2000/01/rdf-schema#label"
+
+
+def _bindings(res: dict[str, Any]) -> list[dict[str, Any]]:
+    return (((res.get("results") or {}).get("bindings")) or [])
+
+
+def _label_score(label_binding: dict[str, Any]) -> int:
+    # Prefer English, then no-language, then anything else.
+    lang = (label_binding.get("xml:lang") or "").lower()
+    if lang == "en":
+        return 3
+    if lang == "":
+        return 2
+    return 1
+
+
+async def _fetch_rdfs_labels_for_iris(
+    sparql: SparqlEngine,
+    iris: list[str],
+    *,
+    batch_size: int = 500,
+) -> dict[str, str]:
+    best: dict[str, tuple[int, str]] = {}
+
+    for i in range(0, len(iris), batch_size):
+        batch = iris[i : i + batch_size]
+        values = " ".join(f"<{u}>" for u in batch)
+        q = f"""
+SELECT ?s ?label
+WHERE {{
+  VALUES ?s {{ {values} }}
+  ?s <{RDFS_LABEL}> ?label .
+}}
+"""
+        res = await sparql.query_json(q)
+        for b in _bindings(res):
+            s = (b.get("s") or {}).get("value")
+            label_term = b.get("label") or {}
+            if not s or label_term.get("type") != "literal":
+                continue
+            label_value = label_term.get("value")
+            if label_value is None:
+                continue
+            score = _label_score(label_term)
+            prev = best.get(s)
+            if prev is None or score > prev[0]:
+                best[s] = (score, str(label_value))
+
+    return {iri: lbl for iri, (_, lbl) in best.items()}
+
+
+async def fetch_graph_snapshot(
+    sparql: SparqlEngine,
+    *,
+    settings: Settings,
+    node_limit: int,
+    edge_limit: int,
+) -> GraphResponse:
+    """
+    Fetch a graph snapshot (nodes + edges) via SPARQL, independent of whether the
+    underlying engine is RDFLib or AnzoGraph.
+    """
+    edges_q = edge_retrieval_query(edge_limit=edge_limit, include_bnodes=settings.include_bnodes)
+    res = await sparql.query_json(edges_q)
+    bindings = (((res.get("results") or {}).get("bindings")) or [])
+    nodes, edges = graph_from_sparql_bindings(
+        bindings,
+        node_limit=node_limit,
+        include_bnodes=settings.include_bnodes,
+    )
+
+    # Add positions so the frontend doesn't need to run a layout.
+    #
+    # We are exporting only rdfs:subClassOf triples. In the exported edges:
+    #   source = subclass, target = superclass
+    # For hierarchical layout we invert edges to:
+    #   superclass -> subclass
+    hier_edges: list[tuple[int, int]] = []
+    for e in edges:
+        s = e.get("source")
+        t = e.get("target")
+        try:
+            sid = int(s)  # subclass
+            tid = int(t)  # superclass
+        except Exception:
+            continue
+        hier_edges.append((tid, sid))
+
+    try:
+        layers = level_synchronous_kahn_layers(node_count=len(nodes), edges=hier_edges)
+    except CycleError as e:
+        # Add a small URI sample to aid debugging.
+        sample: list[str] = []
+        for nid in e.remaining_node_ids[:20]:
+            try:
+                sample.append(str(nodes[nid].get("iri")))
+            except Exception:
+                continue
+        raise CycleError(
+            processed=e.processed,
+            total=e.total,
+            remaining_node_ids=e.remaining_node_ids,
+            remaining_iri_sample=sample or None,
+        ) from None
+
+    # Deterministic order within each ring/layer for stable layouts.
+    id_to_iri = [str(n.get("iri", "")) for n in nodes]
+    for layer in layers:
+        layer.sort(key=lambda nid: id_to_iri[nid])
+
+    xs, ys = radial_positions_from_layers(node_count=len(nodes), layers=layers)
+    for i, node in enumerate(nodes):
+        node["x"] = float(xs[i])
+        node["y"] = float(ys[i])
+
+    # Attach labels for URI nodes (blank nodes remain label-less).
+    uri_nodes = [n for n in nodes if n.get("termType") == "uri"]
+    if uri_nodes:
+        iris = [str(n["iri"]) for n in uri_nodes if isinstance(n.get("iri"), str)]
+        label_by_iri = await _fetch_rdfs_labels_for_iris(sparql, iris)
+        for n in uri_nodes:
+            iri = n.get("iri")
+            if isinstance(iri, str) and iri in label_by_iri:
+                n["label"] = label_by_iri[iri]
+
+    meta = GraphResponse.Meta(
+        backend=sparql.name,
+        ttl_path=settings.ttl_path if settings.graph_backend == "rdflib" else None,
+        sparql_endpoint=settings.effective_sparql_endpoint() if settings.graph_backend == "anzograph" else None,
+        include_bnodes=settings.include_bnodes,
+        node_limit=node_limit,
+        edge_limit=edge_limit,
+        nodes=len(nodes),
+        edges=len(edges),
+    )
+    return GraphResponse(nodes=nodes, edges=edges, meta=meta)

backend/app/pipelines/layout_dag_radial.py

@@ -0,0 +1,141 @@
+from __future__ import annotations
+
+import math
+from collections import deque
+from typing import Iterable, Sequence
+
+
+class CycleError(RuntimeError):
+    """
+    Raised when the requested layout requires a DAG, but a cycle is detected.
+
+    `remaining_node_ids` are the node ids that still had indegree > 0 after Kahn.
+    """
+
+    def __init__(
+        self,
+        *,
+        processed: int,
+        total: int,
+        remaining_node_ids: list[int],
+        remaining_iri_sample: list[str] | None = None,
+    ) -> None:
+        self.processed = int(processed)
+        self.total = int(total)
+        self.remaining_node_ids = remaining_node_ids
+        self.remaining_iri_sample = remaining_iri_sample
+
+        msg = f"Cycle detected in subClassOf graph (processed {self.processed}/{self.total} nodes)."
+        if remaining_iri_sample:
+            msg += f" Example nodes: {', '.join(remaining_iri_sample)}"
+        super().__init__(msg)
+
+
+def level_synchronous_kahn_layers(
+    *,
+    node_count: int,
+    edges: Iterable[tuple[int, int]],
+) -> list[list[int]]:
+    """
+    Level-synchronous Kahn's algorithm:
+    - process the entire current queue as one batch (one layer)
+    - only then enqueue newly-unlocked nodes for the next batch
+
+    `edges` are directed (u -> v).
+    """
+    n = int(node_count)
+    if n <= 0:
+        return []
+
+    adj: list[list[int]] = [[] for _ in range(n)]
+    indeg = [0] * n
+
+    for u, v in edges:
+        if u == v:
+            # Self-loops don't help layout and would trivially violate DAG-ness.
+            continue
+        if not (0 <= u < n and 0 <= v < n):
+            continue
+        adj[u].append(v)
+        indeg[v] += 1
+
+    q: deque[int] = deque(i for i, d in enumerate(indeg) if d == 0)
+    layers: list[list[int]] = []
+
+    processed = 0
+    while q:
+        # Consume the full current queue as a single layer.
+        layer = list(q)
+        q.clear()
+        layers.append(layer)
+
+        for u in layer:
+            processed += 1
+            for v in adj[u]:
+                indeg[v] -= 1
+                if indeg[v] == 0:
+                    q.append(v)
+
+    if processed != n:
+        remaining = [i for i, d in enumerate(indeg) if d > 0]
+        raise CycleError(processed=processed, total=n, remaining_node_ids=remaining)
+
+    return layers
+
+
+def radial_positions_from_layers(
+    *,
+    node_count: int,
+    layers: Sequence[Sequence[int]],
+    max_r: float = 5000.0,
+) -> tuple[list[float], list[float]]:
+    """
+    Assign node positions in concentric rings (one ring per layer).
+
+    - radius increases with layer index
+    - nodes within a layer are placed evenly by angle
+    - each ring gets a "golden-angle" rotation to reduce spoke artifacts
+    """
+    n = int(node_count)
+    if n <= 0:
+        return ([], [])
+
+    xs = [0.0] * n
+    ys = [0.0] * n
+    if not layers:
+        return (xs, ys)
+
+    two_pi = 2.0 * math.pi
+    golden = math.pi * (3.0 - math.sqrt(5.0))
+
+    layer_count = len(layers)
+    denom = float(layer_count + 1)
+
+    for li, layer in enumerate(layers):
+        m = len(layer)
+        if m <= 0:
+            continue
+
+        # Keep everything within ~[-max_r, max_r] like the previous spiral layout.
+        r = ((li + 1) / denom) * max_r
+
+        # Rotate each layer deterministically to avoid radial spokes aligning.
+        offset = (li * golden) % two_pi
+
+        if m == 1:
+            nid = int(layer[0])
+            if 0 <= nid < n:
+                xs[nid] = r * math.cos(offset)
+                ys[nid] = r * math.sin(offset)
+            continue
+
+        step = two_pi / float(m)
+        for j, raw_id in enumerate(layer):
+            nid = int(raw_id)
+            if not (0 <= nid < n):
+                continue
+            t = offset + step * float(j)
+            xs[nid] = r * math.cos(t)
+            ys[nid] = r * math.sin(t)
+
+    return (xs, ys)

backend/app/pipelines/layout_spiral.py

@@ -0,0 +1,30 @@
+from __future__ import annotations
+
+import math
+
+
+def spiral_positions(n: int, *, max_r: float = 5000.0) -> tuple[list[float], list[float]]:
+    """
+    Deterministic "sunflower" (golden-angle) spiral layout.
+
+    This is intentionally simple and stable across runs:
+    - angle increments by the golden angle to avoid radial spokes
+    - radius grows with sqrt(i) to keep density roughly uniform over area
+    """
+    if n <= 0:
+        return ([], [])
+
+    xs = [0.0] * n
+    ys = [0.0] * n
+
+    golden = math.pi * (3.0 - math.sqrt(5.0))
+    denom = float(max(1, n - 1))
+
+    for i in range(n):
+        t = i * golden
+        r = math.sqrt(i / denom) * max_r
+        xs[i] = r * math.cos(t)
+        ys[i] = r * math.sin(t)
+
+    return xs, ys
+

backend/app/pipelines/owl_imports_combiner.py

@@ -0,0 +1,96 @@
+from __future__ import annotations
+
+import logging
+import os
+from pathlib import Path
+from urllib.parse import unquote, urlparse
+
+from rdflib import Graph
+from rdflib.namespace import OWL
+
+
+logger = logging.getLogger(__name__)
+
+
+def _is_http_url(location: str) -> bool:
+    scheme = urlparse(location).scheme.lower()
+    return scheme in {"http", "https"}
+
+
+def _is_file_uri(location: str) -> bool:
+    return urlparse(location).scheme.lower() == "file"
+
+
+def _file_uri_to_path(location: str) -> Path:
+    u = urlparse(location)
+    if u.scheme.lower() != "file":
+        raise ValueError(f"Not a file:// URI: {location!r}")
+    return Path(unquote(u.path))
+
+
+def resolve_output_location(
+    entry_location: str,
+    *,
+    output_location: str | None,
+    output_name: str,
+) -> str:
+    if output_location:
+        return output_location
+
+    if _is_http_url(entry_location):
+        raise ValueError(
+            "COMBINE_ENTRY_LOCATION points to an http(s) URL; set COMBINE_OUTPUT_LOCATION to a writable file path."
+        )
+
+    entry_path = _file_uri_to_path(entry_location) if _is_file_uri(entry_location) else Path(entry_location)
+    return str(entry_path.parent / output_name)
+
+
+def _output_destination_to_path(output_location: str) -> Path:
+    if _is_file_uri(output_location):
+        return _file_uri_to_path(output_location)
+    if _is_http_url(output_location):
+        raise ValueError("Output location must be a local file path (or file:// URI), not http(s).")
+    return Path(output_location)
+
+
+def output_location_to_path(output_location: str) -> Path:
+    return _output_destination_to_path(output_location)
+
+
+def build_combined_graph(entry_location: str) -> Graph:
+    """
+    Recursively loads an RDF document (file path, file:// URI, or http(s) URL) and its
+    owl:imports into a single in-memory graph.
+    """
+    combined_graph = Graph()
+    visited_locations: set[str] = set()
+
+    def resolve_imports(location: str) -> None:
+        if location in visited_locations:
+            return
+        visited_locations.add(location)
+
+        logger.info("Loading ontology: %s", location)
+        try:
+            combined_graph.parse(location=location)
+        except Exception as e:
+            logger.warning("Failed to load %s (%s)", location, e)
+            return
+
+        imports = [str(o) for _, _, o in combined_graph.triples((None, OWL.imports, None))]
+        for imported_location in imports:
+            if imported_location not in visited_locations:
+                resolve_imports(imported_location)
+
+    resolve_imports(entry_location)
+    return combined_graph
+
+
+def serialize_graph_to_ttl(graph: Graph, output_location: str) -> None:
+    output_path = _output_destination_to_path(output_location)
+    output_path.parent.mkdir(parents=True, exist_ok=True)
+
+    tmp_path = output_path.with_suffix(output_path.suffix + ".tmp")
+    graph.serialize(destination=str(tmp_path), format="turtle")
+    os.replace(str(tmp_path), str(output_path))

backend/app/pipelines/selection_neighbors.py

@@ -0,0 +1,137 @@
+from __future__ import annotations
+
+from typing import Any, Iterable
+
+from ..models import GraphResponse, Node
+from ..sparql_engine import SparqlEngine
+
+
+def _values_term(node: Node) -> str | None:
+    iri = node.iri
+    if node.termType == "uri":
+        return f"<{iri}>"
+    if node.termType == "bnode":
+        if iri.startswith("_:"):
+            return iri
+        return f"_:{iri}"
+    return None
+
+
+def selection_neighbors_query(*, selected_nodes: Iterable[Node], include_bnodes: bool) -> str:
+    values_terms: list[str] = []
+    for n in selected_nodes:
+        t = _values_term(n)
+        if t is None:
+            continue
+        values_terms.append(t)
+
+    if not values_terms:
+        # Caller should avoid running this query when selection is empty, but keep this safe.
+        return "SELECT ?nbr WHERE { FILTER(false) }"
+
+    bnode_filter = "" if include_bnodes else "FILTER(!isBlank(?nbr))"
+    values = " ".join(values_terms)
+
+    # Neighbors are defined as any node directly connected by rdf:type (to owl:Class)
+    # or rdfs:subClassOf, in either direction (treating edges as undirected).
+    return f"""
+PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
+PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
+PREFIX owl: <http://www.w3.org/2002/07/owl#>
+
+SELECT DISTINCT ?nbr
+WHERE {{
+  VALUES ?sel {{ {values} }}
+  {{
+    ?sel rdf:type ?o .
+    ?o rdf:type owl:Class .
+    BIND(?o AS ?nbr)
+  }}
+  UNION
+  {{
+    ?s rdf:type ?sel .
+    ?sel rdf:type owl:Class .
+    BIND(?s AS ?nbr)
+  }}
+  UNION
+  {{
+    ?sel rdfs:subClassOf ?o .
+    BIND(?o AS ?nbr)
+  }}
+  UNION
+  {{
+    ?s rdfs:subClassOf ?sel .
+    BIND(?s AS ?nbr)
+  }}
+  FILTER(!isLiteral(?nbr))
+  FILTER(?nbr != ?sel)
+  {bnode_filter}
+}}
+"""
+
+
+def _bindings(res: dict[str, Any]) -> list[dict[str, Any]]:
+    return (((res.get("results") or {}).get("bindings")) or [])
+
+
+def _term_key(term: dict[str, Any], *, include_bnodes: bool) -> tuple[str, str] | None:
+    t = term.get("type")
+    v = term.get("value")
+    if not t or v is None:
+        return None
+    if t == "literal":
+        return None
+    if t == "bnode":
+        if not include_bnodes:
+            return None
+        return ("bnode", f"_:{v}")
+    return ("uri", str(v))
+
+
+async def fetch_neighbor_ids_for_selection(
+    sparql: SparqlEngine,
+    *,
+    snapshot: GraphResponse,
+    selected_ids: list[int],
+    include_bnodes: bool,
+) -> list[int]:
+    id_to_node: dict[int, Node] = {n.id: n for n in snapshot.nodes}
+
+    selected_nodes: list[Node] = []
+    selected_id_set: set[int] = set()
+    for nid in selected_ids:
+        if not isinstance(nid, int):
+            continue
+        n = id_to_node.get(nid)
+        if n is None:
+            continue
+        if n.termType == "bnode" and not include_bnodes:
+            continue
+        selected_nodes.append(n)
+        selected_id_set.add(nid)
+
+    if not selected_nodes:
+        return []
+
+    key_to_id: dict[tuple[str, str], int] = {}
+    for n in snapshot.nodes:
+        key_to_id[(n.termType, n.iri)] = n.id
+
+    q = selection_neighbors_query(selected_nodes=selected_nodes, include_bnodes=include_bnodes)
+    res = await sparql.query_json(q)
+
+    neighbor_ids: set[int] = set()
+    for b in _bindings(res):
+        nbr_term = b.get("nbr") or {}
+        key = _term_key(nbr_term, include_bnodes=include_bnodes)
+        if key is None:
+            continue
+        nid = key_to_id.get(key)
+        if nid is None:
+            continue
+        if nid in selected_id_set:
+            continue
+        neighbor_ids.add(nid)
+
+    # Stable ordering for consistent frontend behavior.
+    return sorted(neighbor_ids)

backend/app/pipelines/snapshot_service.py

@@ -0,0 +1,63 @@
+from __future__ import annotations
+
+import asyncio
+from dataclasses import dataclass
+
+from ..models import GraphResponse
+from ..sparql_engine import SparqlEngine
+from ..settings import Settings
+from .graph_snapshot import fetch_graph_snapshot
+
+
+@dataclass(frozen=True)
+class SnapshotKey:
+    node_limit: int
+    edge_limit: int
+    include_bnodes: bool
+
+
+class GraphSnapshotService:
+    """
+    Caches graph snapshots so the backend doesn't re-run expensive SPARQL for stats/graph.
+    """
+
+    def __init__(self, *, sparql: SparqlEngine, settings: Settings):
+        self._sparql = sparql
+        self._settings = settings
+
+        self._cache: dict[SnapshotKey, GraphResponse] = {}
+        self._locks: dict[SnapshotKey, asyncio.Lock] = {}
+        self._global_lock = asyncio.Lock()
+
+    async def get(self, *, node_limit: int, edge_limit: int) -> GraphResponse:
+        key = SnapshotKey(
+            node_limit=node_limit,
+            edge_limit=edge_limit,
+            include_bnodes=self._settings.include_bnodes,
+        )
+
+        cached = self._cache.get(key)
+        if cached is not None:
+            return cached
+
+        # Create/get a per-key lock under a global lock to avoid races.
+        async with self._global_lock:
+            lock = self._locks.get(key)
+            if lock is None:
+                lock = asyncio.Lock()
+                self._locks[key] = lock
+
+        async with lock:
+            cached2 = self._cache.get(key)
+            if cached2 is not None:
+                return cached2
+
+            snapshot = await fetch_graph_snapshot(
+                self._sparql,
+                settings=self._settings,
+                node_limit=node_limit,
+                edge_limit=edge_limit,
+            )
+            self._cache[key] = snapshot
+            return snapshot
+

backend/app/pipelines/subclass_labels.py

@@ -0,0 +1,153 @@
+from __future__ import annotations
+
+from typing import Any
+
+from ..sparql_engine import SparqlEngine
+
+RDFS_SUBCLASS_OF = "http://www.w3.org/2000/01/rdf-schema#subClassOf"
+RDFS_LABEL = "http://www.w3.org/2000/01/rdf-schema#label"
+
+
+def _bindings(res: dict[str, Any]) -> list[dict[str, Any]]:
+    return (((res.get("results") or {}).get("bindings")) or [])
+
+
+def _term_key(term: dict[str, Any]) -> tuple[str, str] | None:
+    t = term.get("type")
+    v = term.get("value")
+    if not t or v is None:
+        return None
+    if t == "literal":
+        return None
+    if t == "bnode":
+        return ("bnode", str(v))
+    return ("uri", str(v))
+
+
+def _key_to_entity_string(key: tuple[str, str]) -> str:
+    t, v = key
+    if t == "bnode":
+        return f"_:{v}"
+    return v
+
+
+def _label_score(binding: dict[str, Any]) -> int:
+    """
+    Higher is better.
+    Prefer English, then no-language, then anything else.
+    """
+    lang = (binding.get("xml:lang") or "").lower()
+    if lang == "en":
+        return 3
+    if lang == "":
+        return 2
+    return 1
+
+
+async def extract_subclass_entities_and_labels(
+    sparql: SparqlEngine,
+    *,
+    include_bnodes: bool,
+    label_batch_size: int = 500,
+) -> tuple[list[str], list[str | None]]:
+    """
+    Pipeline:
+      1) Query all rdfs:subClassOf triples.
+      2) Build a unique set of entity terms from subjects+objects, convert to list.
+      3) Fetch rdfs:label for those entities and return an aligned labels list.
+
+    Returns:
+      entities: list[str] (IRI or "_:bnodeId")
+      labels:   list[str|None], aligned with entities
+    """
+
+    subclass_q = f"""
+SELECT ?s ?o
+WHERE {{
+  ?s <{RDFS_SUBCLASS_OF}> ?o .
+  FILTER(!isLiteral(?o))
+  {"FILTER(!isBlank(?s) && !isBlank(?o))" if not include_bnodes else ""}
+}}
+"""
+    res = await sparql.query_json(subclass_q)
+
+    entity_keys: set[tuple[str, str]] = set()
+    for b in _bindings(res):
+        sk = _term_key(b.get("s") or {})
+        ok = _term_key(b.get("o") or {})
+        if sk is not None and (include_bnodes or sk[0] != "bnode"):
+            entity_keys.add(sk)
+        if ok is not None and (include_bnodes or ok[0] != "bnode"):
+            entity_keys.add(ok)
+
+    # Deterministic ordering.
+    entity_key_list = sorted(entity_keys, key=lambda k: (k[0], k[1]))
+    entities = [_key_to_entity_string(k) for k in entity_key_list]
+
+    # Build label map keyed by term key.
+    best_label_by_key: dict[tuple[str, str], tuple[int, str]] = {}
+
+    # URIs can be batch-queried via VALUES.
+    uri_values = [v for (t, v) in entity_key_list if t == "uri"]
+    for i in range(0, len(uri_values), label_batch_size):
+        batch = uri_values[i : i + label_batch_size]
+        values = " ".join(f"<{u}>" for u in batch)
+        labels_q = f"""
+SELECT ?s ?label
+WHERE {{
+  VALUES ?s {{ {values} }}
+  ?s <{RDFS_LABEL}> ?label .
+}}
+"""
+        lres = await sparql.query_json(labels_q)
+        for b in _bindings(lres):
+            sk = _term_key(b.get("s") or {})
+            if sk is None or sk[0] != "uri":
+                continue
+            label_term = b.get("label") or {}
+            if label_term.get("type") != "literal":
+                continue
+            label_value = label_term.get("value")
+            if label_value is None:
+                continue
+
+            score = _label_score(label_term)
+            prev = best_label_by_key.get(sk)
+            if prev is None or score > prev[0]:
+                best_label_by_key[sk] = (score, str(label_value))
+
+    # Blank nodes can't reliably be addressed by ID across queries, but if enabled we can still
+    # fetch all bnode labels and filter locally.
+    if include_bnodes:
+        bnode_keys = {k for k in entity_key_list if k[0] == "bnode"}
+        if bnode_keys:
+            bnode_labels_q = f"""
+SELECT ?s ?label
+WHERE {{
+  ?s <{RDFS_LABEL}> ?label .
+  FILTER(isBlank(?s))
+}}
+"""
+            blres = await sparql.query_json(bnode_labels_q)
+            for b in _bindings(blres):
+                sk = _term_key(b.get("s") or {})
+                if sk is None or sk not in bnode_keys:
+                    continue
+                label_term = b.get("label") or {}
+                if label_term.get("type") != "literal":
+                    continue
+                label_value = label_term.get("value")
+                if label_value is None:
+                    continue
+                score = _label_score(label_term)
+                prev = best_label_by_key.get(sk)
+                if prev is None or score > prev[0]:
+                    best_label_by_key[sk] = (score, str(label_value))
+
+    labels: list[str | None] = []
+    for k in entity_key_list:
+        item = best_label_by_key.get(k)
+        labels.append(item[1] if item else None)
+
+    return entities, labels
+

backend/app/rdf_store.py

@@ -0,0 +1,150 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Any
+
+from rdflib import BNode, Graph, Literal, URIRef
+from rdflib.namespace import RDFS, SKOS
+
+
+LABEL_PREDICATES = {RDFS.label, SKOS.prefLabel, SKOS.altLabel}
+
+
+@dataclass(frozen=True)
+class EdgeRow:
+    source: int
+    target: int
+    predicate: str
+
+
+class RDFStore:
+    def __init__(self, *, ttl_path: str, include_bnodes: bool, max_triples: int | None):
+        self.ttl_path = ttl_path
+        self.include_bnodes = include_bnodes
+        self.max_triples = max_triples
+
+        self.graph: Graph | None = None
+
+        self._id_by_term: dict[Any, int] = {}
+        self._term_by_id: list[Any] = []
+
+        self._labels_by_id: dict[int, str] = {}
+        self._edges: list[EdgeRow] = []
+        self._parsed_triples = 0
+
+    def _term_allowed(self, term: Any) -> bool:
+        if isinstance(term, Literal):
+            return False
+        if isinstance(term, BNode) and not self.include_bnodes:
+            return False
+        return isinstance(term, (URIRef, BNode))
+
+    def _get_id(self, term: Any) -> int | None:
+        if not self._term_allowed(term):
+            return None
+        existing = self._id_by_term.get(term)
+        if existing is not None:
+            return existing
+        nid = len(self._term_by_id)
+        self._id_by_term[term] = nid
+        self._term_by_id.append(term)
+        return nid
+
+    def _term_type(self, term: Any) -> str:
+        if isinstance(term, BNode):
+            return "bnode"
+        return "uri"
+
+    def _term_iri(self, term: Any) -> str:
+        if isinstance(term, BNode):
+            return f"_:{term}"
+        return str(term)
+
+    def load(self, graph: Graph | None = None) -> None:
+        g = graph or Graph()
+        if graph is None:
+            g.parse(self.ttl_path, format="turtle")
+        self.graph = g
+
+        self._id_by_term.clear()
+        self._term_by_id.clear()
+        self._labels_by_id.clear()
+        self._edges.clear()
+
+        parsed = 0
+        for (s, p, o) in g:
+            parsed += 1
+            if self.max_triples is not None and parsed > self.max_triples:
+                break
+
+            # Capture labels but do not emit them as edges.
+            if p in LABEL_PREDICATES and isinstance(o, Literal):
+                sid = self._get_id(s)
+                if sid is not None and sid not in self._labels_by_id:
+                    self._labels_by_id[sid] = str(o)
+                continue
+
+            sid = self._get_id(s)
+            oid = self._get_id(o)
+            if sid is None or oid is None:
+                continue
+
+            self._edges.append(EdgeRow(source=sid, target=oid, predicate=str(p)))
+
+        self._parsed_triples = parsed
+
+    @property
+    def parsed_triples(self) -> int:
+        return self._parsed_triples
+
+    @property
+    def node_count(self) -> int:
+        return len(self._term_by_id)
+
+    @property
+    def edge_count(self) -> int:
+        return len(self._edges)
+
+    def node_slice(self, *, offset: int, limit: int) -> list[dict[str, Any]]:
+        end = min(self.node_count, offset + limit)
+        out: list[dict[str, Any]] = []
+        for nid in range(offset, end):
+            term = self._term_by_id[nid]
+            out.append(
+                {
+                    "id": nid,
+                    "termType": self._term_type(term),
+                    "iri": self._term_iri(term),
+                    "label": self._labels_by_id.get(nid),
+                }
+            )
+        return out
+
+    def edge_slice(self, *, offset: int, limit: int) -> list[dict[str, Any]]:
+        end = min(self.edge_count, offset + limit)
+        out: list[dict[str, Any]] = []
+        for row in self._edges[offset:end]:
+            out.append(
+                {
+                    "source": row.source,
+                    "target": row.target,
+                    "predicate": row.predicate,
+                }
+            )
+        return out
+
+    def edges_within_nodes(self, *, max_node_id_exclusive: int, limit: int) -> list[dict[str, Any]]:
+        out: list[dict[str, Any]] = []
+        for row in self._edges:
+            if row.source >= max_node_id_exclusive or row.target >= max_node_id_exclusive:
+                continue
+            out.append(
+                {
+                    "source": row.source,
+                    "target": row.target,
+                    "predicate": row.predicate,
+                }
+            )
+            if len(out) >= limit:
+                break
+        return out

backend/app/settings.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+from typing import Literal
+
+from pydantic import Field
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    # Which graph engine executes SPARQL queries.
+    # - rdflib: parse TTL locally and query in-memory
+    # - anzograph: query a remote AnzoGraph SPARQL endpoint (optionally LOAD on startup)
+    graph_backend: Literal["rdflib", "anzograph"] = Field(default="rdflib", alias="GRAPH_BACKEND")
+
+    ttl_path: str = Field(default="/data/o3po.ttl", alias="TTL_PATH")
+    include_bnodes: bool = Field(default=False, alias="INCLUDE_BNODES")
+    max_triples: int | None = Field(default=None, alias="MAX_TRIPLES")
+
+    # Optional: Combine owl:imports into a single TTL file on backend startup.
+    combine_owl_imports_on_start: bool = Field(default=False, alias="COMBINE_OWL_IMPORTS_ON_START")
+    combine_entry_location: str | None = Field(default=None, alias="COMBINE_ENTRY_LOCATION")
+    combine_output_location: str | None = Field(default=None, alias="COMBINE_OUTPUT_LOCATION")
+    combine_output_name: str = Field(default="combined_ontology.ttl", alias="COMBINE_OUTPUT_NAME")
+    combine_force: bool = Field(default=False, alias="COMBINE_FORCE")
+
+    # AnzoGraph / SPARQL endpoint configuration
+    sparql_host: str = Field(default="http://anzograph:8080", alias="SPARQL_HOST")
+    # If not set, the backend uses `${SPARQL_HOST}/sparql`.
+    sparql_endpoint: str | None = Field(default=None, alias="SPARQL_ENDPOINT")
+    sparql_user: str | None = Field(default=None, alias="SPARQL_USER")
+    sparql_pass: str | None = Field(default=None, alias="SPARQL_PASS")
+
+    # File URI as seen by the AnzoGraph container (used with SPARQL `LOAD`).
+    # Example: file:///opt/shared-files/o3po.ttl
+    sparql_data_file: str | None = Field(default=None, alias="SPARQL_DATA_FILE")
+    sparql_graph_iri: str | None = Field(default=None, alias="SPARQL_GRAPH_IRI")
+    sparql_load_on_start: bool = Field(default=False, alias="SPARQL_LOAD_ON_START")
+    sparql_clear_on_start: bool = Field(default=False, alias="SPARQL_CLEAR_ON_START")
+
+    sparql_timeout_s: float = Field(default=300.0, alias="SPARQL_TIMEOUT_S")
+    sparql_ready_retries: int = Field(default=30, alias="SPARQL_READY_RETRIES")
+    sparql_ready_delay_s: float = Field(default=4.0, alias="SPARQL_READY_DELAY_S")
+    sparql_ready_timeout_s: float = Field(default=10.0, alias="SPARQL_READY_TIMEOUT_S")
+
+    # Comma-separated, or "*" (default).
+    cors_origins: str = Field(default="*", alias="CORS_ORIGINS")
+
+    model_config = SettingsConfigDict(env_file=".env", extra="ignore")
+
+    def cors_origin_list(self) -> list[str]:
+        if self.cors_origins.strip() == "*":
+            return ["*"]
+        return [o.strip() for o in self.cors_origins.split(",") if o.strip()]
+
+    def effective_sparql_endpoint(self) -> str:
+        if self.sparql_endpoint and self.sparql_endpoint.strip():
+            return self.sparql_endpoint.strip()
+        return self.sparql_host.rstrip("/") + "/sparql"

backend/app/sparql_engine.py

@@ -0,0 +1,177 @@
+from __future__ import annotations
+
+import asyncio
+import base64
+import json
+from typing import Any, Protocol
+
+import httpx
+from rdflib import Graph
+
+from .settings import Settings
+
+
+class SparqlEngine(Protocol):
+    name: str
+
+    async def startup(self) -> None: ...
+
+    async def shutdown(self) -> None: ...
+
+    async def query_json(self, query: str) -> dict[str, Any]: ...
+
+
+class RdflibEngine:
+    name = "rdflib"
+
+    def __init__(self, *, ttl_path: str, graph: Graph | None = None):
+        self.ttl_path = ttl_path
+        self.graph: Graph | None = graph
+
+    async def startup(self) -> None:
+        if self.graph is not None:
+            return
+        g = Graph()
+        g.parse(self.ttl_path, format="turtle")
+        self.graph = g
+
+    async def shutdown(self) -> None:
+        # Nothing to close for in-memory rdflib graph.
+        return None
+
+    async def query_json(self, query: str) -> dict[str, Any]:
+        if self.graph is None:
+            raise RuntimeError("RdflibEngine not started")
+
+        result = self.graph.query(query)
+        payload = result.serialize(format="json")
+        if isinstance(payload, bytes):
+            payload = payload.decode("utf-8")
+        return json.loads(payload)
+
+
+class AnzoGraphEngine:
+    name = "anzograph"
+
+    def __init__(self, *, settings: Settings):
+        self.endpoint = settings.effective_sparql_endpoint()
+        self.timeout_s = settings.sparql_timeout_s
+        self.ready_retries = settings.sparql_ready_retries
+        self.ready_delay_s = settings.sparql_ready_delay_s
+        self.ready_timeout_s = settings.sparql_ready_timeout_s
+
+        self.user = settings.sparql_user
+        self.password = settings.sparql_pass
+        self.data_file = settings.sparql_data_file
+        self.graph_iri = settings.sparql_graph_iri
+        self.load_on_start = settings.sparql_load_on_start
+        self.clear_on_start = settings.sparql_clear_on_start
+
+        self._client: httpx.AsyncClient | None = None
+        self._auth_header = self._build_auth_header(self.user, self.password)
+
+    @staticmethod
+    def _build_auth_header(user: str | None, password: str | None) -> str | None:
+        if not user or not password:
+            return None
+        token = base64.b64encode(f"{user}:{password}".encode("utf-8")).decode("ascii")
+        return f"Basic {token}"
+
+    async def startup(self) -> None:
+        self._client = httpx.AsyncClient(timeout=self.timeout_s)
+
+        await self._wait_ready()
+
+        if self.clear_on_start:
+            await self._update("CLEAR ALL")
+            await self._wait_ready()
+
+        if self.load_on_start:
+            if not self.data_file:
+                raise RuntimeError("SPARQL_LOAD_ON_START=true but SPARQL_DATA_FILE is not set")
+
+            if self.graph_iri:
+                await self._update(f"LOAD <{self.data_file}> INTO GRAPH <{self.graph_iri}>")
+            else:
+                await self._update(f"LOAD <{self.data_file}>")
+
+            # AnzoGraph may still be indexing after LOAD.
+            await self._wait_ready()
+
+    async def shutdown(self) -> None:
+        if self._client is not None:
+            await self._client.aclose()
+            self._client = None
+
+    async def query_json(self, query: str) -> dict[str, Any]:
+        if self._client is None:
+            raise RuntimeError("AnzoGraphEngine not started")
+
+        headers = {
+            "Content-Type": "application/x-www-form-urlencoded",
+            "Accept": "application/sparql-results+json",
+        }
+        if self._auth_header:
+            headers["Authorization"] = self._auth_header
+
+        # AnzoGraph expects x-www-form-urlencoded with `query=...`.
+        resp = await self._client.post(
+            self.endpoint,
+            headers=headers,
+            data={"query": query},
+        )
+        resp.raise_for_status()
+        return resp.json()
+
+    async def _update(self, update: str) -> None:
+        if self._client is None:
+            raise RuntimeError("AnzoGraphEngine not started")
+
+        headers = {
+            "Content-Type": "application/sparql-update",
+            "Accept": "application/json",
+        }
+        if self._auth_header:
+            headers["Authorization"] = self._auth_header
+
+        resp = await self._client.post(self.endpoint, headers=headers, content=update)
+        resp.raise_for_status()
+
+    async def _wait_ready(self) -> None:
+        if self._client is None:
+            raise RuntimeError("AnzoGraphEngine not started")
+
+        # Match the repo's Julia readiness gate: real SPARQL POST + valid JSON parse.
+        headers = {
+            "Content-Type": "application/x-www-form-urlencoded",
+            "Accept": "application/sparql-results+json",
+        }
+        if self._auth_header:
+            headers["Authorization"] = self._auth_header
+
+        last_err: Exception | None = None
+        for _ in range(self.ready_retries):
+            try:
+                resp = await self._client.post(
+                    self.endpoint,
+                    headers=headers,
+                    data={"query": "ASK WHERE { ?s ?p ?o }"},
+                    timeout=self.ready_timeout_s,
+                )
+                resp.raise_for_status()
+                # Ensure it's JSON, not HTML/text during boot.
+                resp.json()
+                return
+            except Exception as e:
+                last_err = e
+                await asyncio.sleep(self.ready_delay_s)
+
+        raise RuntimeError(f"AnzoGraph not ready at {self.endpoint}") from last_err
+
+
+def create_sparql_engine(settings: Settings, *, rdflib_graph: Graph | None = None) -> SparqlEngine:
+    if settings.graph_backend == "rdflib":
+        return RdflibEngine(ttl_path=settings.ttl_path, graph=rdflib_graph)
+    if settings.graph_backend == "anzograph":
+        return AnzoGraphEngine(settings=settings)
+    raise RuntimeError(f"Unsupported GRAPH_BACKEND={settings.graph_backend!r}")

backend/requirements.txt

@@ -0,0 +1,5 @@
+fastapi
+uvicorn[standard]
+rdflib
+pydantic-settings
+httpx

docker-compose.yml

@@ -1,9 +1,60 @@
 services:
-  app:
-    build: .
+  backend:
+    build: ./backend
+    ports:
+      - "8000:8000"
+    environment:
+      - GRAPH_BACKEND=${GRAPH_BACKEND:-rdflib}
+      - TTL_PATH=${TTL_PATH:-/data/o3po.ttl}
+      - INCLUDE_BNODES=${INCLUDE_BNODES:-false}
+      - MAX_TRIPLES
+      - CORS_ORIGINS=${CORS_ORIGINS:-http://localhost:5173}
+      - SPARQL_HOST=${SPARQL_HOST:-http://anzograph:8080}
+      - SPARQL_ENDPOINT
+      - SPARQL_USER=${SPARQL_USER:-admin}
+      - SPARQL_PASS=${SPARQL_PASS:-Passw0rd1}
+      - SPARQL_DATA_FILE=${SPARQL_DATA_FILE:-file:///opt/shared-files/o3po.ttl}
+      - SPARQL_GRAPH_IRI
+      - SPARQL_LOAD_ON_START=${SPARQL_LOAD_ON_START:-false}
+      - SPARQL_CLEAR_ON_START=${SPARQL_CLEAR_ON_START:-false}
+      - SPARQL_TIMEOUT_S=${SPARQL_TIMEOUT_S:-300}
+      - SPARQL_READY_RETRIES=${SPARQL_READY_RETRIES:-30}
+      - SPARQL_READY_DELAY_S=${SPARQL_READY_DELAY_S:-4}
+      - SPARQL_READY_TIMEOUT_S=${SPARQL_READY_TIMEOUT_S:-10}
+      - COMBINE_OWL_IMPORTS_ON_START=${COMBINE_OWL_IMPORTS_ON_START:-false}
+      - COMBINE_ENTRY_LOCATION
+      - COMBINE_OUTPUT_LOCATION
+      - COMBINE_OUTPUT_NAME
+      - COMBINE_FORCE=${COMBINE_FORCE:-false}
+    volumes:
+      - ./backend:/app
+      - ./data:/data:Z
+    command: uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload
+    healthcheck:
+      test: ["CMD", "python", "-c", "import urllib.request; urllib.request.urlopen('http://localhost:8000/api/health').read()"]
+      interval: 5s
+      timeout: 3s
+      retries: 60
+
+  frontend:
+    build: ./frontend
     ports:
       - "5173:5173"
-    command: sh -c "npx tsx scripts/compute_layout.ts && npm run dev -- --host"
+    environment:
+      - VITE_BACKEND_URL=${VITE_BACKEND_URL:-http://backend:8000}
     volumes:
-      - .:/app
-      - /app/node_modules # Prevents local node_modules from overwriting the container's
+      - ./frontend:/app
+      - /app/node_modules
+    depends_on:
+      - backend
+    # Docker Compose v1 doesn't support depends_on:condition. Do an explicit wait here.
+    command: sh -c "until wget -qO- http://backend:8000/api/health >/dev/null 2>&1; do echo 'waiting for backend...'; sleep 1; done; npm run dev -- --host --port 5173"
+  
+  anzograph:
+    image: cambridgesemantics/anzograph:latest
+    container_name: anzograph
+    ports:
+      - "8080:8080"
+      - "8443:8443"
+    volumes:
+      - ./data:/opt/shared-files:Z

frontend/Dockerfile

@@ -2,6 +2,8 @@ FROM node:lts-alpine
 
 WORKDIR /app
 
+EXPOSE 5173
+
 # Copy dependency definitions
 COPY package*.json ./
 
@@ -11,8 +13,5 @@ RUN npm install
 # Copy the rest of the source code
 COPY . .
 
-# Expose the standard Vite port
-EXPOSE 5173
-
-# Compute layout, then start the dev server with --host for external access
-CMD ["sh", "-c", "npm run layout && npm run dev -- --host"]
+# Start the dev server with --host for external access
+CMD ["npm", "run", "dev", "--", "--host", "--port", "5173"]

frontend/src/App.tsx

@@ -1,10 +1,25 @@
 import { useEffect, useRef, useState } from "react";
 import { Renderer } from "./renderer";
 
+function sleep(ms: number): Promise<void> {
+  return new Promise((r) => setTimeout(r, ms));
+}
+
+type GraphMeta = {
+  backend?: string;
+  ttl_path?: string | null;
+  sparql_endpoint?: string | null;
+  include_bnodes?: boolean;
+  node_limit?: number;
+  edge_limit?: number;
+  nodes?: number;
+  edges?: number;
+};
+
 export default function App() {
   const canvasRef = useRef<HTMLCanvasElement>(null);
   const rendererRef = useRef<Renderer | null>(null);
-  const [status, setStatus] = useState("Loading node positions…");
+  const [status, setStatus] = useState("Waiting for backend…");
   const [nodeCount, setNodeCount] = useState(0);
   const [stats, setStats] = useState({
     fps: 0,
@@ -14,11 +29,15 @@ export default function App() {
     ptSize: 0,
   });
   const [error, setError] = useState("");
-  const [hoveredNode, setHoveredNode] = useState<{ x: number; y: number; screenX: number; screenY: number } | null>(null);
+  const [hoveredNode, setHoveredNode] = useState<{ x: number; y: number; screenX: number; screenY: number; label?: string; iri?: string } | null>(null);
   const [selectedNodes, setSelectedNodes] = useState<Set<number>>(new Set());
+  const [backendStats, setBackendStats] = useState<{ nodes: number; edges: number; backend?: string } | null>(null);
+  const graphMetaRef = useRef<GraphMeta | null>(null);
+  const neighborsReqIdRef = useRef(0);
 
   // Store mouse position in a ref so it can be accessed in render loop without re-renders
   const mousePos = useRef({ x: 0, y: 0 });
+  const nodesRef = useRef<any[]>([]);
 
   useEffect(() => {
     const canvas = canvasRef.current;
@@ -35,55 +54,82 @@ export default function App() {
 
     let cancelled = false;
 
-    // Fetch CSVs, parse, and init renderer
     (async () => {
       try {
-        setStatus("Fetching data files…");
-        const [nodesResponse, edgesResponse] = await Promise.all([
-          fetch("/node_positions.csv"),
-          fetch("/edges.csv"),
-        ]);
-        if (!nodesResponse.ok) throw new Error(`Failed to fetch nodes: ${nodesResponse.status}`);
-        if (!edgesResponse.ok) throw new Error(`Failed to fetch edges: ${edgesResponse.status}`);
+        // Wait for backend (docker-compose also gates startup via healthcheck, but this
+        // handles running the frontend standalone).
+        const deadline = performance.now() + 180_000;
+        let attempt = 0;
+        while (performance.now() < deadline) {
+          attempt++;
+          setStatus(`Waiting for backend… (attempt ${attempt})`);
+          try {
+            const res = await fetch("/api/health");
+            if (res.ok) break;
+          } catch {
+            // ignore and retry
+          }
+          await sleep(1000);
+          if (cancelled) return;
+        }
 
-        const [nodesText, edgesText] = await Promise.all([
-          nodesResponse.text(),
-          edgesResponse.text(),
-        ]);
+        setStatus("Fetching graph…");
+        const graphRes = await fetch("/api/graph");
+        if (!graphRes.ok) throw new Error(`Failed to fetch graph: ${graphRes.status}`);
+        const graph = await graphRes.json();
         if (cancelled) return;
 
-        setStatus("Parsing positions…");
-        const nodeLines = nodesText.split("\n").slice(1).filter(l => l.trim().length > 0);
-        const count = nodeLines.length;
+        const nodes = Array.isArray(graph.nodes) ? graph.nodes : [];
+        const edges = Array.isArray(graph.edges) ? graph.edges : [];
+        const meta = graph.meta || null;
+        const count = nodes.length;
 
+        nodesRef.current = nodes;
+        graphMetaRef.current = meta && typeof meta === "object" ? (meta as GraphMeta) : null;
+
+        // Build positions from backend-provided node coordinates.
+        setStatus("Preparing buffers…");
         const xs = new Float32Array(count);
         const ys = new Float32Array(count);
+        for (let i = 0; i < count; i++) {
+          const nx = nodes[i]?.x;
+          const ny = nodes[i]?.y;
+          xs[i] = typeof nx === "number" ? nx : 0;
+          ys[i] = typeof ny === "number" ? ny : 0;
+        }
         const vertexIds = new Uint32Array(count);
         for (let i = 0; i < count; i++) {
-          const parts = nodeLines[i].split(",");
-          vertexIds[i] = parseInt(parts[0], 10);
-          xs[i] = parseFloat(parts[1]);
-          ys[i] = parseFloat(parts[2]);
+          const id = nodes[i]?.id;
+          vertexIds[i] = typeof id === "number" ? id >>> 0 : i;
         }
 
-        setStatus("Parsing edges…");
-        const edgeLines = edgesText.split("\n").slice(1).filter(l => l.trim().length > 0);
-        const edgeData = new Uint32Array(edgeLines.length * 2);
-        for (let i = 0; i < edgeLines.length; i++) {
-          const parts = edgeLines[i].split(",");
-          edgeData[i * 2] = parseInt(parts[0], 10);
-          edgeData[i * 2 + 1] = parseInt(parts[1], 10);
+        // Build edges as vertex-id pairs.
+        const edgeData = new Uint32Array(edges.length * 2);
+        for (let i = 0; i < edges.length; i++) {
+          const s = edges[i]?.source;
+          const t = edges[i]?.target;
+          edgeData[i * 2] = typeof s === "number" ? s >>> 0 : 0;
+          edgeData[i * 2 + 1] = typeof t === "number" ? t >>> 0 : 0;
         }
 
-        if (cancelled) return;
+        // Use /api/graph meta; don't do a second expensive backend call.
+        if (meta && typeof meta.nodes === "number" && typeof meta.edges === "number") {
+          setBackendStats({
+            nodes: meta.nodes,
+            edges: meta.edges,
+            backend: typeof meta.backend === "string" ? meta.backend : undefined,
+          });
+        } else {
+          setBackendStats({ nodes: nodes.length, edges: edges.length });
+        }
 
         setStatus("Building spatial index…");
-        await new Promise(r => setTimeout(r, 0));
+        await new Promise((r) => setTimeout(r, 0));
 
         const buildMs = renderer.init(xs, ys, vertexIds, edgeData);
         setNodeCount(renderer.getNodeCount());
         setStatus("");
-        console.log(`Init complete: ${count.toLocaleString()} nodes, ${edgeLines.length.toLocaleString()} edges in ${buildMs.toFixed(0)}ms`);
+        console.log(`Init complete: ${count.toLocaleString()} nodes, ${edges.length.toLocaleString()} edges in ${buildMs.toFixed(0)}ms`);
       } catch (e) {
         if (!cancelled) {
           setError(e instanceof Error ? e.message : String(e));
@@ -167,9 +213,18 @@ export default function App() {
       frameCount++;
 
       // Find hovered node using quadtree
-      const node = renderer.findNodeAt(mousePos.current.x, mousePos.current.y);
-      if (node) {
-        setHoveredNode({ ...node, screenX: mousePos.current.x, screenY: mousePos.current.y });
+      const hit = renderer.findNodeIndexAt(mousePos.current.x, mousePos.current.y);
+      if (hit) {
+        const origIdx = renderer.sortedIndexToOriginalIndex(hit.index);
+        const meta = origIdx === null ? null : nodesRef.current[origIdx];
+        setHoveredNode({
+          x: hit.x,
+          y: hit.y,
+          screenX: mousePos.current.x,
+          screenY: mousePos.current.y,
+          label: meta && typeof meta.label === "string" ? meta.label : undefined,
+          iri: meta && typeof meta.iri === "string" ? meta.iri : undefined,
+        });
       } else {
         setHoveredNode(null);
       }
@@ -205,9 +260,72 @@ export default function App() {
 
   // Sync selection state to renderer
   useEffect(() => {
-    if (rendererRef.current) {
-      rendererRef.current.updateSelection(selectedNodes);
+    const renderer = rendererRef.current;
+    if (!renderer) return;
+
+    // Optimistically reflect selection immediately; neighbors will be filled in by backend.
+    renderer.updateSelection(selectedNodes, new Set());
+
+    // Invalidate any in-flight neighbor request for the previous selection.
+    const reqId = ++neighborsReqIdRef.current;
+
+    // Convert selected sorted indices to backend node IDs (graph-export dense IDs).
+    const selectedIds: number[] = [];
+    for (const sortedIdx of selectedNodes) {
+      const origIdx = renderer.sortedIndexToOriginalIndex(sortedIdx);
+      if (origIdx === null) continue;
+      const nodeId = nodesRef.current?.[origIdx]?.id;
+      if (typeof nodeId === "number") selectedIds.push(nodeId);
     }
+
+    if (selectedIds.length === 0) {
+      return;
+    }
+
+    // Always send the full current selection list; backend returns the merged neighbor set.
+    const ctrl = new AbortController();
+
+    (async () => {
+      try {
+        const meta = graphMetaRef.current;
+        const body = {
+          selected_ids: selectedIds,
+          node_limit: typeof meta?.node_limit === "number" ? meta.node_limit : undefined,
+          edge_limit: typeof meta?.edge_limit === "number" ? meta.edge_limit : undefined,
+        };
+
+        const res = await fetch("/api/neighbors", {
+          method: "POST",
+          headers: { "content-type": "application/json" },
+          body: JSON.stringify(body),
+          signal: ctrl.signal,
+        });
+        if (!res.ok) throw new Error(`POST /api/neighbors failed: ${res.status}`);
+        const data = await res.json();
+        if (ctrl.signal.aborted) return;
+        if (reqId !== neighborsReqIdRef.current) return;
+
+        const neighborIds: unknown = data?.neighbor_ids;
+        const neighborSorted = new Set<number>();
+        if (Array.isArray(neighborIds)) {
+          for (const id of neighborIds) {
+            if (typeof id !== "number") continue;
+            const sorted = renderer.vertexIdToSortedIndexOrNull(id);
+            if (sorted === null) continue;
+            if (!selectedNodes.has(sorted)) neighborSorted.add(sorted);
+          }
+        }
+
+        renderer.updateSelection(selectedNodes, neighborSorted);
+      } catch (e) {
+        if (ctrl.signal.aborted) return;
+        console.warn(e);
+        // Keep the UI usable even if neighbors fail to load.
+        renderer.updateSelection(selectedNodes, new Set());
+      }
+    })();
+
+    return () => ctrl.abort();
   }, [selectedNodes]);
 
   return (
@@ -279,6 +397,11 @@ export default function App() {
             <div>Zoom: {stats.zoom < 0.01 ? stats.zoom.toExponential(2) : stats.zoom.toFixed(2)} px/unit</div>
             <div>Pt Size: {stats.ptSize.toFixed(1)}px</div>
             <div style={{ color: "#f80" }}>Selected: {selectedNodes.size}</div>
+            {backendStats && (
+              <div style={{ color: "#8f8" }}>
+                Backend{backendStats.backend ? ` (${backendStats.backend})` : ""}: {backendStats.nodes.toLocaleString()} nodes, {backendStats.edges.toLocaleString()} edges
+              </div>
+            )}
           </div>
           <div
             style={{
@@ -316,7 +439,12 @@ export default function App() {
                 boxShadow: "0 2px 8px rgba(0,0,0,0.5)",
               }}
             >
-              ({hoveredNode.x.toFixed(2)}, {hoveredNode.y.toFixed(2)})
+              <div style={{ color: "#0ff" }}>
+                {hoveredNode.label || hoveredNode.iri || "(unknown)"}
+              </div>
+              <div style={{ color: "#688" }}>
+                ({hoveredNode.x.toFixed(2)}, {hoveredNode.y.toFixed(2)})
+              </div>
             </div>
           )}
         </>

frontend/src/renderer.ts

@@ -80,9 +80,11 @@ export class Renderer {
   // Data
   private leaves: Leaf[] = [];
   private sorted: Float32Array = new Float32Array(0);
+  // order[sortedIdx] = originalIdx (original ordering matches input arrays)
+  private sortedToOriginal: Uint32Array = new Uint32Array(0);
+  private vertexIdToSortedIndex: Map<number, number> = new Map();
   private nodeCount = 0;
   private edgeCount = 0;
-  private neighborMap: Map<number, number[]> = new Map();
   private leafEdgeStarts: Uint32Array = new Uint32Array(0);
   private leafEdgeCounts: Uint32Array = new Uint32Array(0);
   private maxPtSize = 256;
@@ -202,6 +204,7 @@ export class Renderer {
     const { sorted, leaves, order } = buildSpatialIndex(xs, ys);
     this.leaves = leaves;
     this.sorted = sorted;
+    this.sortedToOriginal = order;
 
     // Pre-allocate arrays for render loop (zero-allocation rendering)
     this.visibleLeafIndices = new Uint32Array(leaves.length);
@@ -226,6 +229,13 @@ export class Renderer {
       originalToSorted[order[i]] = i;
     }
 
+    // Build vertex ID → sorted index mapping (used by backend-driven neighbor highlighting)
+    const vertexIdToSortedIndex = new Map<number, number>();
+    for (let i = 0; i < count; i++) {
+      vertexIdToSortedIndex.set(vertexIds[i], originalToSorted[i]);
+    }
+    this.vertexIdToSortedIndex = vertexIdToSortedIndex;
+
     // Remap edges from vertex IDs to sorted indices
     const lineIndices = new Uint32Array(edgeCount * 2);
     let validEdges = 0;
@@ -241,18 +251,6 @@ export class Renderer {
     }
     this.edgeCount = validEdges;
 
-    // Build per-node neighbor list from edges for selection queries
-    const neighborMap = new Map<number, number[]>();
-    for (let i = 0; i < validEdges; i++) {
-      const src = lineIndices[i * 2];
-      const dst = lineIndices[i * 2 + 1];
-      if (!neighborMap.has(src)) neighborMap.set(src, []);
-      neighborMap.get(src)!.push(dst);
-      if (!neighborMap.has(dst)) neighborMap.set(dst, []);
-      neighborMap.get(dst)!.push(src);
-    }
-    this.neighborMap = neighborMap;
-
     // Build per-leaf edge index for efficient visible-only edge drawing
     // Find which leaf each sorted index belongs to
     const nodeToLeaf = new Uint32Array(count);
@@ -331,6 +329,28 @@ export class Renderer {
     return this.nodeCount;
   }
 
+  /**
+   * Map a sorted buffer index (what findNodeIndexAt returns) back to the original
+   * index in the input arrays used to initialize the renderer.
+   */
+  sortedIndexToOriginalIndex(sortedIndex: number): number | null {
+    if (
+      sortedIndex < 0 ||
+      sortedIndex >= this.sortedToOriginal.length
+    ) {
+      return null;
+    }
+    return this.sortedToOriginal[sortedIndex];
+  }
+
+  /**
+   * Convert a backend node ID (node.id from /api/graph) to a sorted index used by the renderer.
+   */
+  vertexIdToSortedIndexOrNull(vertexId: number): number | null {
+    const idx = this.vertexIdToSortedIndex.get(vertexId);
+    return typeof idx === "number" ? idx : null;
+  }
+
   /**
    * Convert screen coordinates (CSS pixels) to world coordinates.
    */
@@ -412,10 +432,10 @@ export class Renderer {
 
   /**
    * Update the selection buffer with the given set of node indices.
-   * Also computes neighbors of selected nodes.
-   * Call this whenever React's selection state changes.
+   * Neighbor indices are provided by the backend (SPARQL query) and uploaded separately.
+   * Call this whenever selection or backend neighbor results change.
    */
-  updateSelection(selectedIndices: Set<number>): void {
+  updateSelection(selectedIndices: Set<number>, neighborIndices: Set<number> = new Set()): void {
     const gl = this.gl;
 
     // Upload selected indices
@@ -425,23 +445,11 @@ export class Renderer {
     gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, indices, gl.DYNAMIC_DRAW);
     gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);
 
-    // Compute neighbors of selected nodes (excluding already selected)
-    const neighborSet = new Set<number>();
-    for (const nodeIdx of selectedIndices) {
-      const nodeNeighbors = this.neighborMap.get(nodeIdx);
-      if (!nodeNeighbors) continue;
-      for (const n of nodeNeighbors) {
-        if (!selectedIndices.has(n)) {
-          neighborSet.add(n);
-        }
-      }
-    }
-
     // Upload neighbor indices
-    const neighborIndices = new Uint32Array(neighborSet);
-    this.neighborCount = neighborIndices.length;
+    const neighborIndexArray = new Uint32Array(neighborIndices);
+    this.neighborCount = neighborIndexArray.length;
     gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, this.neighborIbo);
-    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, neighborIndices, gl.DYNAMIC_DRAW);
+    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, neighborIndexArray, gl.DYNAMIC_DRAW);
     gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);
   }
 

frontend/vite.config.ts

@@ -16,4 +16,10 @@ export default defineConfig({
       "@": path.resolve(__dirname, "src"),
     },
   },
+  server: {
+    proxy: {
+      // Backend is reachable as http://backend:8000 inside docker-compose; localhost outside.
+      "/api": process.env.VITE_BACKEND_URL || "http://localhost:8000",
+    },
+  },
 });