PortalJS — Add DCAT

Overview

Turn an existing PortalJS (portaljs-catalog) portal into a harvestable data catalog. PortalJS is Frictionless-native — a dataset is a Data Package (see portaljs-define-schema) — and DCAT is the serialization + harvest layer on top (lib/metadata/dcat.ts + lib/metadata/dcat-profiles.ts). This skill selects one or more DCAT application profiles, maps every dataset's metadata to them, and writes static feed files at build time — JSON-LD, Turtle, and RDF/XML — so external catalogs (data.europa.eu, data.gov, national portals) can harvest the datasets automatically, on any static host, with no runtime.

Prerequisites

• A scaffolded PortalJS portal with datasets.json, package.json, and lib/metadata/ (the metadata-profile contract) present.
• lib/metadata/dcat.ts (the DCAT-3 core) already in place — profiles augment it.
• Node 18+ and npm available in the portal directory.
• For DCAT-AP / DCAT-US: a publishing organization (name + homepage) and a contact (name + email) — both profiles require dct:publisher and dcat:contactPoint.
• Optional but recommended: network access to run SHACL conformance checks against the official EU ITB validator or pyshacl.

Instructions

The canonical, full step-by-step workflow is .claude/commands/portaljs-add-dcat.md — the single source of truth. Read and follow it when executing. Summary:

1. Gather input from $ARGUMENTS (interview if thin): portal directory (default .), profiles (default ["dcat-3"]), site URL, publisher, contact, license, themes, languages, access level.
2. Validate the portal directory: confirm datasets.json, package.json, and lib/metadata/ exist; stop with an ERROR: if the metadata contract is missing.
3. Ensure the DCAT profile layer is present — dcat-profiles.ts, dcat-rdf.ts, dcat-validate.ts — copying canonical versions from examples/portaljs-catalog if the portal predates this skill.
4. Ensure scripts/generate-dcat.ts is wired to predev/prebuild and emits per-profile x serialization feeds from dcat.config.json.
5. Write dcat.config.json with the gathered profiles, publisher, contact, license, themes, and access level.
6. Add feed autodiscovery: a <link rel="alternate" type="application/ld+json"> to pages/_document.tsx pointing at /catalog.jsonld.
7. Generate the feeds and check conformance: run npm run generate:dcat and surface any missing mandatory fields.
8. Verify the RDF: confirm the JSON-LD parses, and cross-check that JSON-LD, Turtle, and RDF/XML agree; run SHACL validation (ITB for DCAT-AP, pyshacl for DCAT-US) when network/tooling allow.
9. Verify the build with npx next build; fix errors before reporting success.
10. Report the profiles emitted, feed paths, conformance status, and next steps (register with the harvester, run portaljs-deploy).

Output

• Created/modified: dcat.config.json (committed config).
• Generated (build artifacts, gitignored): public/catalog.jsonld /.ttl/.rdf (canonical feed), public/catalog.<profile>.{jsonld,ttl,rdf} per configured profile, public/catalog-feeds.json (feed index).
• Modified: pages/_document.tsx (autodiscovery <link>), package.json (generate:dcat script wired to predev/prebuild).
• Verified: feeds are valid JSON-LD/Turtle/RDF-XML, conformance status reported, npx next build passes.

Error Handling

Symptom	Cause	Fix
NO_METADATA_CONTRACT	lib/metadata/ not found	Portal predates the metadata-profile contract; scaffold with portaljs-new-portal or add lib/metadata first.
NO_DCAT_CORE	lib/metadata/dcat.ts not found	The DCAT-3 core is missing; update the portal template before adding profiles.
BAD_CONFIG	dcat.config.json is not valid JSON	Fix the syntax and re-run npm run generate:dcat.
UNKNOWN_PROFILE	Profile id not in the registry	Use one of dcat-2, dcat-3, dcat-ap, dcat-us, geodcat-ap, croissant, dcat-ap-se, dcat-ap-ch, dcat-ap-de, or register a national profile first.
Feed flagged non-conformant	publisher/contactPoint missing for DCAT-AP or DCAT-US	Ask the user for the publishing organization and contact, add to dcat.config.json, regenerate.
DCAT-US SHACL rejects the publisher	Publisher has no IRI (blank node)	Set publisher.uri (or homepage) in dcat.config.json.
next build fails after config change	Malformed JSON in dcat.config.json or datasets.json	Print the build log, fix the JSON, rebuild before reporting success.

Examples

Example 1 — Default DCAT-3 feed, no national harvesting

/portaljs-add-dcat

Emits the canonical public/catalog.jsonld/.ttl/.rdf under the default dcat-3 profile, adds autodiscovery to _document.tsx, and wires generate:dcat into predev/prebuild. No publisher/contact required.

Example 2 — EU harvesting via DCAT-AP

/portaljs-add-dcat profiles=dcat-ap site=https://data.example.org

Prompts for publisher (name + homepage) and contact (name + email) since DCAT-AP requires both, writes them into dcat.config.json, and emits public/catalog.dcat-ap.{jsonld,ttl,rdf} plus the canonical feed with absolute links.

Example 3 — US federal harvesting via DCAT-US

/portaljs-add-dcat profiles=dcat-us site=https://data.example.gov

Requires an IRI-identified publisher (publisher.uri) for SHACL conformance; emits catalog.dcat-us.{jsonld,ttl,rdf} and validates against the DCAT-US 3.0 SHACL shapes with pyshacl when available.

Example 4 — Multiple profiles plus a national extension

/portaljs-add-dcat profiles=dcat-ap,dcat-ap-de site=https://daten.example.de

Emits both catalog.dcat-ap.* and catalog.dcat-ap-de.* feeds from one config; the first profile listed also becomes the canonical, un-suffixed catalog.jsonld/.ttl/.rdf.

Resources

• Full workflow: .claude/commands/portaljs-add-dcat.md
• Profile registry, serialization formats, and validator details: references/reference.md
• Related skills: portaljs-define-schema, portaljs-new-portal, portaljs-deploy, portaljs-migrate
• DCAT specification: https://www.w3.org/TR/vocab-dcat-3/