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:
- Gather input from
$ARGUMENTS (interview if thin): portal directory (default .),
profiles (default ["dcat-3"]), site URL, publisher, contact, license, themes,
languages, access level.
- Validate the portal directory: confirm
datasets.json, package.json, and
lib/metadata/ exist; stop with an ERROR: if the metadata contract is missing.
- 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.
- Ensure
scripts/generate-dcat.ts is wired to predev/prebuild and emits
per-profile x serialization feeds from dcat.config.json.
- Write
dcat.config.json with the gathered profiles, publisher, contact, license,
themes, and access level.
- Add feed autodiscovery: a
<link rel="alternate" type="application/ld+json"> to
pages/_document.tsx pointing at /catalog.jsonld.
- Generate the feeds and check conformance: run
npm run generate:dcat and surface
any missing mandatory fields.
- 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.
- Verify the build with
npx next build; fix errors before reporting success.
- 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