DCAT

The catalogue has the capability to convert ISO to DCAT format in various API endpoint.

Supported DCAT profiles

A base conversion is provided with complementary extensions for various profiles of DCAT:

Profile	Version	Description	URL	Conversion from
W3C DCAT	3	Default W3C standard	https://www.w3.org/TR/vocab-dcat-3/	ISO19115-3
European DCAT-AP	3.0.0	DCAT profile for sharing information about Catalogues containing Datasets and Data Services descriptions in Europe	https://semiceu.github.io/DCAT-AP/releases/3.0.0/	ISO19115-3
European DCAT-AP-Mobility	1.0.1	mobilityDCAT-AP is a mobility-related extension of the DCAT-AP	https://mobilitydcat-ap.github.io/mobilityDCAT-AP/releases/	ISO19115-3
European DCAT-AP-HVD	2.2.0	DCAT-AP for a dataset that is subject to the requirements imposed by the High-Value Dataset implementing regulation	https://semiceu.github.io/DCAT-AP/releases/2.2.0-hvd/	ISO19115-3
European GeoDCAT-AP	3.0.0		https://semiceu.github.io/GeoDCAT-AP/releases/3.0.0/	ISO19115-3
European GeoDCAT-AP (SEMIC)	3.0.0	XSLT conversion maintained by SEMIC	https://semiceu.github.io/GeoDCAT-AP/releases/3.0.0/	ISO19139

The mapping is done from ISO19115-3 to DCAT* except for the SEMIC conversion which converts ISO19139 to GeoDCAT-AP.
When needed, an ISO19139 to or from ISO19115-3 conversion is applied (eg. a CSW request querying a catalog in ISO19115-3 using the SEMIC conversion).
DCAT output are not available for ISO19110 or Dublin core standards.

Past implementation

The first implementation of DCAT output was done in 2012 and was targeting interaction with semantic service and semantic sitemap support. DCAT output was available using a service named rdf.search. This service was deprecated in version 4.0.0 in favor of producing DCAT output in the Catalog Service for the Web (CSW) or using the formatters API.

Usage in the formatters API

Each DCAT formats are available using a formatter eg. http://localhost:8080/geonetwork/srv/api/records/be44fe5a-65ca-4b70-9d29-ac5bf1f0ebc5/formatters/eu-dcat-ap

To add the formatter in the record view download list, the user interface configuration can be updated:

User interface configuration:

{
  "mods": {
    "search": {
      "downloadFormatter": [
        {
          "label": "exportMEF",
          "url": "/formatters/zip?withRelated=false",
          "class": "fa-file-zip-o"
        },
        {
          "label": "exportPDF",
          "url": "/formatters/xsl-view?output=pdf&language=${lang}",
          "class": "fa-file-pdf-o"
        },
        {
          "label": "exportXML",
          "url": "/formatters/xml",
          "class": "fa-file-code-o"
        },
        {
          "label": "W3C-DCAT",
          "url": "/formatters/dcat"
        },
        {
          "label": "EU-DCAT-AP",
          "url": "/formatters/eu-dcat-ap"
        },
        {
          "label": "EU-GEO-DCAT-AP",
          "url": "/formatters/eu-geodcat-ap"
        },
        {
          "label": "EU-DCAT-AP-MOBILITY",
          "url": "/formatters/eu-dcat-ap-mobility"
        },
        {
          "label": "EU-DCAT-AP-HVD",
          "url": "/formatters/eu-dcat-ap-hvd"
        }
      ]

Usage in the CSW service

All DCAT profiles are also accessible using CSW protocol.

A GetRecordById operation can be used: http://localhost:8080/geonetwork/srv/eng/csw?SERVICE=CSW&VERSION=2.0.2&REQUEST=GetRecordById&ID=da165110-88fd-11da-a88f-000d939bc5d8&outputSchema=https://semiceu.github.io/DCAT-AP/releases/2.2.0-hvd/ and is equivalent to the API http://localhost:8080/geonetwork/srv/api/records/da165110-88fd-11da-a88f-000d939bc5d8/formatters/eu-dcat-ap-hvd?output=xml.

A GetRecords operation can be used to retrieve a set of records: http://localhost:8080/geonetwork/srv/fre/csw?SERVICE=CSW&VERSION=2.0.2&REQUEST=GetRecords&outputSchema=http://data.europa.eu/930/&elementSetName=full&resultType=results&maxRecords=300

Use the outputSchema parameter to select the DCAT profile to use. The following values are supported:

Profile	Output schema parameter
CSW	http://www.opengis.net/cat/csw/2.0.2
ISO19115-3	http://standards.iso.org/iso/19115/-3/mdb/2.0
ISO19110	http://www.isotc211.org/2005/gfc
ISO19139	http://www.isotc211.org/2005/gmd
W3C DCAT	http://www.w3.org/ns/dcat#core
EU-DCAT-AP	http://data.europa.eu/r5r/
EU-GeoDCAT-AP	http://data.europa.eu/930/
EU-GeoDCAT-AP (SEMIC)	http://data.europa.eu/930/#semiceu
DCAT (past implementation - deprecated)	http://www.w3.org/ns/dcat#
EU-DCAT-AP-HVD	https://semiceu.github.io/DCAT-AP/releases/2.2.0-hvd/
EU-DCAT-AP-Mobility	https://w3id.org/mobilitydcat-ap

When using GET request, it is recommended to encode URL characters in parameters (eg. # as %23) to avoid issues with the URL.

Those values are listed in the GetCapabilities operation http://localhost:8080/geonetwork/srv/eng/csw?SERVICE=CSW&VERSION=2.0.2&REQUEST=GetCapabilities.

<ows:Parameter name="outputSchema">
  <ows:Value>http://www.opengis.net/cat/csw/2.0.2</ows:Value>
  <ows:Value>http://standards.iso.org/iso/19115/-3/mdb/2.0</ows:Value>
  <ows:Value>http://www.isotc211.org/2005/gfc</ows:Value>
  <ows:Value>http://www.isotc211.org/2005/gmd</ows:Value>
  <ows:Value>http://data.europa.eu/930/</ows:Value>
  <ows:Value>http://data.europa.eu/930/#semiceu</ows:Value>
  <ows:Value>http://data.europa.eu/r5r/</ows:Value>
  <ows:Value>http://www.w3.org/ns/dcat#</ows:Value>
  <ows:Value>http://www.w3.org/ns/dcat#core</ows:Value>
  <ows:Value>https://semiceu.github.io/DCAT-AP/releases/2.2.0-hvd/</ows:Value>
  <ows:Value>https://w3id.org/mobilitydcat-ap</ows:Value>

Usage in OGC API Records

For the time being, OGC API Records provides a simplified DCAT output (based on the index document).

DCAT validation

The DCAT validation can be done using online validation tool:

https://www.itb.ec.europa.eu/shacl/dcat-ap/upload

Depending on the target DCAT profile to use, it may be required to build proper ISO template and metadata record containing all required fields. Usually profiles are adding constraints for usage of specific vocabularies and fields (eg. for High Value datasets, specific vocabularies are defined for categories, license, applicable legislations, ...).

Mapping considerations

Items under discussion

The mapping is done from ISO19115-3 to DCAT. The mapping may not cover all usages and may be adapted. This can be done in the iso19115-3.2018 schema plugin in the formatter/dcat* XSLT files.

Some points under discussion are:

Object vs Reference:

Should we use object or reference for some fields (eg. contact, organisation, ...)?
What should be the reference URI?
Where is defined the reference URI in ISO?

eg.

for the CatalogRecord reference URI is the metadataLinkage or the metadataIdentifier.
for the Resource reference URI is the first resource identifier or the CatalogRecord reference URI with #resource suffix.
for an organisation, the URI will be the first value in the following sequence:

(cit:partyIdentifier/*/mcc:code/*/text(),
cit:contactInfo/*/cit:onlineResource/*/cit:linkage/gco:CharacterString/text(),
cit:name/gcx:Anchor/@xlink:href,
@uuid)[1]

Distribution model in DCAT and ISO

In DCAT, a number of properties from the dataset are also defined in the distribution elements. In ISO, an option could be to use multiple transfer options element to create multiple distribution elements with more detailed information in DCAT (eg. transfer size).

In the mapping, should we repeat all the information about the dataset? Should we recommend to use multiple transfer options element in ISO?

No equivalent field in ISO

eg. Where to store spdx:checksum in ISO? Could be considered as an online resource id attribute as the checksum uniquely identify the resource.

Associated resources

Links between resources are not always bidirectional so using the associated API would allow to populate more relations. This is also mitigated when the complete RDF graph of the catalogue is retrieved as it will provide relations from all records.

EU DCAT AP High Value Datasets

When encoding in ISO datasets in the context of DCAT HVD, consider encoding the following properties:

Add a keyword pointing to the legislation http://data.europa.eu/eli/reg_impl/2023/138/oj
Add at least one keyword for the dcatap:hvdCategory from the High-value dataset categories vocabulary

See DCAT AP HVD specification for other requirements.

EU DCAT mobility

When encoding in ISO datasets in the context of DCAT Mobility, consider encoding the following properties:

mobilitydcatap:mobilityTheme (mandatory) is encoded as a keyword from the mobility theme vocabulary
mobilitydcatap:georeferencingMethod (recommended) is encoded as a keyword from the mobility georeferencing method vocabulary
mobilitydcatap:networkCoverage (recommended) is encoded as a keyword from the mobility network coverage vocabulary
mobilitydcatap:transportMode (recommended) is encoded as a keyword from the mobility transport mode vocabulary

See DCAT AP Mobility specification for other requirements.

SEMIC conversion compared to GeoNetwork conversion

The main differences between the 2 conversions is that the GeoNetwork conversion starts from ISO19115-3 instead of ISO19139 (to better support additional information provided in ISO19115-3 eg. date lifecycle, party identifiers and citation in data quality, feature catalogue, additional documentation, portrayal sections). The conversion to GeoDCAT-AP is done as an extension of DCAT-AP which extends the core W3C DCAT for easier customization and extension. This allows non EU countries to also use the base DCAT conversion. The conversion is less linear and easier to extend or customize.

SEMIC conversion parameters core, extended, include-deprecated are not available in the GeoNetwork conversion which focus on version 3 of GeoDCAT-AP.

Some of the differences in the GeoNetwork conversion are:

CatalogRecord / dct:identifier is prefixed with the code space if defined.
CatalogRecord / dct:title and dct:description are set at CatalogRecord level and at the Resource level
Resource / First resource identifier is used for dct:identifer (MobilityDCAT restrict it to 0..1), then additional ones are encoded in adms:identifier
Resource / dct:spatial is only encoded using a dcat:bbox in GeoJSON (instead of WKT and GML and GeoJson and the locn:geometry which was kept for backward compatibility with GeoDCAT-AP v1.*)
Resource / dct:temporal is only encoded using a dcat:startDate and dcat:endDate (and do not add same information in schemas:startDate and schemas:endDate which was kept for backward compatibility with GeoDCAT-AP v1.*)
Portrayal, specification, report online link are encoded using foaf:page instead of foaf:landingPage
prov:qualifiedAttribution element are not created because dcat:creator|publisher|contactPoint|.. already provide the same information.
Keyword / When encoded with Anchor, dcat:theme encoded with only a reference in SEMIC conversion and using skos:Concept in the GeoNetwork conversion (see discussion point above)

<dcat:theme rdf:resource="https://metawal.wallonie.be/thesaurus/theme-geoportail-wallon#SubThemesGeoportailWallon/5099"/>
vs
<dcat:theme>
  <skos:Concept rdf:about="https://metawal.wallonie.be/thesaurus/theme-geoportail-wallon#SubThemesGeoportailWallon/5099">
    <skos:prefLabel xml:lang="fre">Données de base (autre)</skos:prefLabel>
  </skos:Concept>
</dcat:theme>

Additional properties supported:

CatalogRecord / dct:issued is added if exists in the metadata (added in ISO19115-3)
CatalogRecord / dct:language is added if exists
CatalogRecord / cnt:characterEncoding is added if exists
Resource / graphicOverview is encoded as foaf:page
Resource / Associated resources
Source dataset are encoded using dct:source
Associated resource are encoded using dct:relation and subtypes (eg. isPartOf)
Party identifier (added in ISO19115-3) are used for rdf:about attribute for individual or organization

Technical differences:

normalize-space is not applied to abstract or lineage (which lose the line breaks and basic formatting)