Add support for DCAT-AP 2.1

[seitenbau-govdata]

We want to add support for the following DCAT-AP 2.1 properties (covers #168):

• dcat:Dataset
  • dcat:bbox und dcat:centroid (in dct:Location of dct:spatial)
  • dcat:startDate, dcat:endDate, time:hasBeginning, time:hasEnd (in dct:PeriodOfTime of dct:temporal)
  • dcat:spatialResolutionInMeters
  • dcat:temporalResolution
  • dct:isReferencedBy
  • prov:wasGeneratedBy
• dcat:Distribution
  • dcatap:availability
  • dcat:compressFormat
  • dcat:packageFormat
  • odrl:hasPolicy

Specification: https://www.w3.org/TR/vocab-dcat-2/

We start by creating a new DCAT-AP 2 profile (plugin euro_dcat_ap_2) that inherits the profile EuropeanDCATAPProfile (plugin euro_dcat_ap).

[amercader]

@seitenbau-govdata if you restart the failed py2 jobs they should pass now (there was a problem with ckanext-harvest reqs, which is fixed now)

[seitenbau-govdata]

@amercader The pull request is now ready for review. Maybe you have a good idea and suggestion how the new profile could be described and announced/introduced in the documentation.

[seitenbau-govdata]

@amercader I do not want to be annoying. But do you think that you will find some time to have a look at the pull request? Or gladly also someone else if you are too busy or on vacation. Thanks in advance.

[amercader]

Sorry @seitenbau-govdata I'm busy with different open fronts (and school holidays!) but will definitely try to find some time for this. I had a quick look and it looks great.
Do any of these changes break compatibility with DCAT-AP 1.1? ie are there changes in how existing fields where parsed/serialized or this just adds new fields?

[seitenbau-govdata]

@amercader Thanks that you will have a look and this despite the circumstances. There are no breaking changes with DCAT-AP 1.1. Only some fields are added to the graph or stored in the database if the imported graph contains properties supported by DCAT-AP 2.

The only existing properties affected by the changes are the property dct:spatial and dct:temporal.

1. In the property dct:spatial the properties dcat:bbox and dcat:centroid are added within the class dct:Location analogous to locn:geometry.
2. The property dct:temporal is added another time, containing the properties dcat:startDate and dcat:endDate, additionally to the property dct:temporal containing the properties schema:startDate and schema:endDate.

[amercader]

@seitenbau-govdata thanks for your work on this, it all looks good.

In terms of introducing these changes and given they are backwards compatible, I think the best approach would be:

• The new default profile should be the new euro_dcat_ap_2 one. So change it here:
  

  ckanext-dcat/ckanext/dcat/processors.py

  Line 31 in 27db031

  DEFAULT_RDF_PROFILES = ['euro_dcat_ap']

• For users that really want to stick with the old profile, we document how to enable it if they upgrade ckanet-dcat (I'm saying it's "partially compatible with DCAT-AP 2.1" because IIUC your PR does not cover all new fields introduced in DCAT-AP 2 right):

diff --git a/README.md b/README.md
index 0b2c50d..91077c0 100644
--- a/README.md
+++ b/README.md
@@ -670,7 +670,12 @@ In most cases the default profile will provide a good mapping that will cover mo
 need custom logic, you can write a custom to profile that extends or replaces the default one.
 
 The default profile is mostly based in the
-[DCAT application profile for data portals in Europe](https://joinup.ec.europa.eu/asset/dcat_application_profile/description). It is actually fully-compatible with [DCAT-AP v1.1](https://joinup.ec.europa.eu/asset/dcat_application_profile/asset_release/dcat-ap-v11). As mentioned before though, it should be generic enough for most DCAT based representations.
+[DCAT application profile for data portals in Europe](https://joinup.ec.europa.eu/asset/dcat_application_profile/description). It is actually fully-compatible with [DCAT-AP v1.1](https://joinup.ec.europa.eu/asset/dcat_application_profile/asset_release/dcat-ap-v11), and partially compatible with [DCAT-AP v2.1.0](https://joinup.ec.europa.eu/collection/semantic-interoperability-community-semic/solution/dcat-application-profile-data-portals-europe/release/210). As mentioned before though, it should be generic enough for most DCAT based representations.
+
+Sites that want to support a particular version of the DCAT-AP can enable a specific profile using one of the methods below:
+
+* DCAT-AP v2.1.0 (default): `euro_dcat_ap_2`
+* DCAT-AP v1.1.1: `euro_dcat_ap`
 
 This plugin also contains a profile to serialize a CKAN dataset to a [schema.org Dataset](http://schema.org/Dataset) called `schemaorg`. This is especially useful to provide [JSON-LD structured data](#structured-data).

• We mention the change in the CHANGELOG, listing the actual fields added

We can release 1.3.0 after this is merged.

[seitenbau-govdata]

@amercader Thanks for your input. I have changed the default profile and updated the documentation. In addition I have fixed the RDFSerializer tests for the DCAT-AP 1 profile euro_dcat_ap and added some basic tests for the default RDFSerializer.

Feel free to comment the latest changes and/or merge the pull request. 😃

[amercader]

Many thanks @seitenbau-govdata, this is a long requested feature! (even if partially supported)

I won't be able to work on this in the next two weeks. Do you mind doing the new release yourself (basically updating the version, tagging and changelog)? I think 1.3.0 makes sense for this one. Thanks!

[seitenbau-govdata]

@amercader Sure, we can do the new release. 1.3.0 as new version sounds good.