DCAT-AP API endpoints for data.public.lu

Data.public.lu provides all its metadata in the DCAT and DCAT-AP formats, i.e. all data about the data stored or referenced on data.public.lu.

[DCAT (Data Catalog Vocabulary)](https://www.w3.org/TR/vocab-dcat/) is a specification designed to facilitate interoperability between data catalogs published on the Web. This specification has been extended via the [DCAT-AP (DCAT Application Profile for data portals in Europe)](https://joinup.ec.europa.eu/collection/semantic-interoperability-community-semic/solution/dcat-application-profile-data-portals-europe) standard, specifically for data portals in Europe. The serialisation of those vocabularies is mainly done in [RDF (Resource Description Framework)](https://www.w3.org/RDF/).
The implementation of data.public.lu is based on the one of the open source [udata](https://udata.readthedocs.io/en/stable/) platform. 

This API enables the federation of multiple Data portals together, for example, all the datasets published on data.public.lu are also published on data.europa.eu. The DCAT API from data.public.lu is used by the european data portal to federate its metadata. The DCAT standard is thus very important to guarantee the interoperability between all data portals in Europe.

### Usage

#### Full catalog
You can find here a few examples using the `curl` command line tool:

To get all the metadata from the whole catalog hosted on data.public.lu
```
curl https://data.public.lu/catalog.rdf
```

#### Metadata for an organization
To get the metadata of a specific organization, you need first to find its ID. The ID of an organization is the last part of its URL. For the organization "Open data Lëtzebuerg" its URL is `https://data.public.lu/fr/organizations/open-data-letzebuerg/` and its ID is `open-data-letzebuerg`.
To get all the metadata for a given organization, we need to call the following URL, where `{id}` has been replaced by the correct ID: `https://data.public.lu/api/1/organizations/{id}/catalog.rdf` Example:
```
curl https://data.public.lu/api/1/organizations/open-data-letzebuerg/catalog.rdf
```

##### Metadata for a dataset
To get the metadata of a specific dataset, you need first to find its ID. The ID of dataset is the last part of its URL. For the dataset "Digital accessibility monitoring report - 2020-2021" its URL is `https://data.public.lu/fr/datasets/digital-accessibility-monitoring-report-2020-2021/` and its ID is `digital-accessibility-monitoring-report-2020-2021`.
To get all the metadata for a given dataset, we need to call the following URL, where `{id}` has been replaced by the correct ID: `https://data.public.lu/api/1/datasets/{id}/rdf` Example:
```
curl https://data.public.lu/api/1/datasets/digital-accessibility-monitoring-report-2020-2021/rdf
```

### Compatibility with DCAT-AP 2.1.1
The DCAT-AP standard is in constant evolution, so the compatibility of the implementation should be regularly compared with the standard and adapted accordingly. In May 2023, we have done this comparison, and the result is available in the resources below (see document named 'udata 6 dcat-ap implementation status").
In the DCAT-AP model, classes and properties have a priority level which should be respected in every implementation: mandatory, recommended and optional. Our goal is to implement all mandatory classes and properties, and if possible implement all recommended classes and properties which make sense in the context of our open data portal.