RDF DCAT endpoints¶

By default, when the dcat plugin is enabled, the following RDF endpoints are available on your CKAN instance. The schema used on the serializations can be customized using profiles.

To disable the RDF endpoints, you can set the ckanext.dcat.enable_rdf_endpoints option in your ini file.

Dataset endpoints¶

RDF representations of a particular dataset can be accessed using the following endpoint:

https://{ckan-instance-host}/dataset/{dataset-id}.{format}

The extension will determine the RDF serialization format returned. The currently supported values are:

Extension	Format	Media Type
`xml`	RDF/XML	application/rdf+xml
`ttl`	Turtle	text/turtle
`n3`	Notation3	text/n3
`jsonld`	JSON-LD	application/ld+json

The fallback rdf format defaults to RDF/XML.

Here's an example of the different formats:

RDF representations will be advertised using <link rel="alternate"> tags on the <head> section of the dataset page source code, e.g.:

<head>

    <link rel="alternate" type="application/rdf+xml" href="http://demo.ckan.org/dataset/34315559-2b08-44eb-a2e6-ebe9ce1a266b.rdf"/>
    <link rel="alternate" type="text/turtle" href="http://demo.ckan.org/dataset/34315559-2b08-44eb-a2e6-ebe9ce1a266b.ttl"/>
    <!-- ... -->

</head>

Check the RDF DCAT Serializer section for more details about how these are generated and how to customize the output using profiles.

You can specify the profile by using the profiles=<profile1>,<profile2> query parameter on the dataset endpoint (as a comma-separated list):

Catalog endpoint¶

Additionally to the individual dataset representations, the extension also offers a catalog-wide endpoint for retrieving multiple datasets at the same time (the datasets are paginated, see below for details):

https://{ckan-instance-host}/catalog.{format}?[page={page}]&[modified_since={date}]&[profiles={profile1},{profile2}]&[q={query}]&[fq={filter query}]

This endpoint base path can be customized if necessary using the ckanext.dcat.catalog_endpoint configuration option, eg:

ckanext.dcat.catalog_endpoint = /dcat/catalog/{_format}

The custom endpoint must start with a forward slash (/) and contain the {_format} placeholder.

As described previously, the extension will determine the RDF serialization format returned.

http://demo.ckan.org/catalog.rdf
http://demo.ckan.org/catalog.xml
http://demo.ckan.org/catalog.ttl

RDF representations will be advertised using <link rel="alternate"> tags on the <head> section of the catalog homepage and the dataset search page source code, eg:

<head>

    <link rel="alternate" type="application/rdf+xml" href="http://demo.ckan.org/catalog.rdf"/>
    <link rel="alternate" type="application/rdf+xml" href="http://demo.ckan.org/catalog.xml"/>
    <link rel="alternate" type="text/turtle" href="http://demo.ckan.org/catalog.ttl"/>
    <!-- ... -->

</head>

The number of datasets returned is limited. The response will include paging info, serialized using the Hydra vocabulary. The different properties are self-explanatory, and can be used by clients to iterate the catalog:

@prefix hydra: <http://www.w3.org/ns/hydra/core#> .

<http://example.com/catalog.ttl?page=1> a hydra:PagedCollection ;
    hydra:first "http://example.com/catalog.ttl?page=1" ;
    hydra:last "http://example.com/catalog.ttl?page=3" ;
    hydra:next "http://example.com/catalog.ttl?page=2" ;
    hydra:totalItems 283 .

The default number of datasets returned (100) can be modified by CKAN site maintainers using ckanext.dcat.datasets_per_page

The catalog endpoint also supports a modified_since parameter to restrict datasets to those modified from a certain date. The parameter value should be a valid ISO-8601 date:

http://demo.ckan.org/catalog.xml?modified_since=2015-07-24

It is possible to specify the profile(s) to use for the serialization using the profiles parameter:

http://demo.ckan.org/catalog.xml?profiles=euro_dcat_ap,sweden_dcat_ap

To filter the output, the catalog endpoint supports the q and fq parameters to specify a search query or filter query:

http://demo.ckan.org/catalog.xml?q=budget
http://demo.ckan.org/catalog.xml?fq=tags:economy

URIs¶

Whenever possible, URIs are generated for the relevant entities. To try to generate them, the extension will use the first found of the following for each entity:

Catalog:
- ckanext.dcat.base_uri configuration option value. This is the recommended approach. Value should be a valid URI.
- ckan.site_url configuration option value.
- 'http://' + app_instance_uuid configuration option value. This is not recommended, and a warning log message will be shown.
Dataset:
- The value of the uri field (note that this is not included in the default CKAN schema)
- The value of an extra with key uri
- Catalog URI (see above) + '/dataset/' + id field
Resource:
- The value of the uri field (note that this is not included in the default CKAN schema)
- Catalog URI (see above) + '/dataset/' + package_id field + '/resource/ + id field

Note that if you are using the RDF DCAT harvester to import datasets from other catalogs and these define a proper URI for each dataset or resource, these will be stored as uri fields in your instance, and so used when generating serializations for them.

Content negotiation¶

The extension supports returning different representations of the datasets based on the value of the Accept header (Content negotiation). This is turned off by default, to enable it, set ckanext.dcat.enable_content_negotiation.

Note

This feature overrides the CKAN core home page and dataset page view routes, so you probably don't want to enable it if your own extension is also doing it.

When enabled, client applications can request a particular format via the Accept header on requests to the main dataset page, eg:

curl https://{ckan-instance-host}/dataset/{dataset-id} -H Accept:text/turtle

curl https://{ckan-instance-host}/dataset/{dataset-id} -H Accept:"application/rdf+xml; q=1.0, application/ld+json; q=0.6"

This is also supported on the catalog endpoint, in this case when making a request to the CKAN root URL (home page). This won't support the pagination and filter parameters:

curl https://{ckan-instance-host} -H Accept:text/turtle