Graph Projector (Retired) and the Ontology Projectors

Status (2026-10-13): The GraphProjector described in the first section was retired and deleted on 2026-04-24 (agent-MCP redesign, cycle 6). Page frontmatter and body links no longer create Knowledge Graph nodes or edges, and the "Project All Pages" admin button is gone. The components that project data today are the four ontology projectors described below. This page keeps the slug so older links still land somewhere accurate.

What the GraphProjector was

The GraphProjector was a PageFilter registered with the WikiEngine that fired on every page save and projected a page's YAML frontmatter into the Knowledge Graph (kg_nodes / kg_edges). In outline it:

parsed the saved page's frontmatter;
separated list-valued relationship keys from plain property keys with a FrontmatterRelationshipDetector;
upserted the page's own node (node type from the type field, human-authored provenance);
upserted an edge to each relationship target, creating a stub node when the target had no page;
added links_to edges for body links; and
removed stale human-authored edges while leaving ai-inferred and ai-reviewed edges alone.

It was unwired from the engine and its code deleted on 2026-04-24. Migration V012 (retire_graph_projector_links_to_edges) then purged every links_to edge it had written, and later migrations (V027, extended by V030) closed kg_edges.relationship_type to a vocabulary of 21 predicates, which excludes links_to. Wikilink structure now belongs to the Page Graph (see PageGraphVsKnowledgeGraph); the Knowledge Graph holds LLM-extracted entities (see KnowledgeGraphCore).

What projects data today

The wikantik-ontology module (Apache Jena) contains four projectors. They read page metadata and PostgreSQL rows and write RDF into per-resource named graphs of a TDB2 store; they do not parse markdown bodies, and the public /sparql endpoint is read-only.

Projector	Input	RDF it writes
`PageProjector`	A page record (`canonical_id` plus frontmatter)	A page resource at `/id/page/{canonical_id}` typed `wk:Hub`, `wk:Article`, `wk:Reference`, `wk:Runbook` or `wk:DesignDoc`, with `dct:title`, `schema:url`, `dct:description`, `dct:created`, `dct:creator`, and one `dct:subject` for each tag and each cluster membership
`ConceptProjector`	The distinct tags and clusters across all pages	One `skos:Concept` per tag or cluster (with `skos:prefLabel`, in the `wk:WikiConcepts` scheme); a sub-cluster `parent/sub` gets `skos:broader` pointing at its parent
`EntityProjector`	A `kg_nodes` row and its outgoing edges	An entity resource at `/id/entity/{uuid}` typed by its entity class, with `rdfs:label`, `prov:wasAttributedTo` (`wk:MachineAgent` or `wk:HumanAgent` by tier) and `prov:wasDerivedFrom` the source page
`EdgeProjector`	A `kg_edges` row	One `wk:` predicate statement between two entity resources; an edge whose relationship type is outside the 21-predicate vocabulary is skipped and logged

Each page, concept and entity graph is re-projected incrementally (OntologyEventListener on page save, rename and delete; OntologyEntitySync on Knowledge Graph changes), and a nightly rebuild from PostgreSQL acts as a reconciliation backstop. The operator guide is docs/admin/OntologyManagement.md; the layer is summarized in WikantikKnowledgeGraph.

Cluster Hub: Wikantik Platform Development Hub: Architecture, MCP Protocols, and Agent Briefings (wikantik-development)