dcat:Distribution is listed among the mandatory classes of DCAT-AP.
However, the cardinality of dcat:distribution (i.e., the property linking a dataset to its distribution(s)) is 0..n - which makes perfect sense: a dataset may not have a distribution or its distribution(s) may be unknown in a given catalogue.
This may cause confusion.
A possible solution is to say that dcat:Distribution is mandatory if any distribution of the corresponding dataset is available. An example of such cases is provided by INSPIRE, where a few metadata elements are said to be "mandatory if..." [1]. E.g., about the medata element "resource locator":
Mandatory if a URL is available to obtain more information on the resource, and/or access related services.
BTW, also the conformance statement should be modified accordingly. Namely, the following paragraph
Provide descriptions of distributions of datasets in the catalogue, including at least the mandatory properties specified in section 7.4.1
may be revised as follows:
Provide descriptions of distributions, if any, of datasets in the catalogue, including at least the mandatory properties specified in section 7.4.1
Comments
Consideration
This is a more general issue – a sender of data cannot satisfy the requirement that data most be provide if, for some reason, there are no instances of a mandatory class.
Proposed resolution
Relax the requirement in the definition of Mandatory class to add “if such instances exist”
Proposed action
Update specification, with new text replacing the definition of Mandatory class in section 5 by:
“Mandatory class: a receiver of data MUST be able to process information about instances of the class; a sender of data MUST provide information about instances of the class, if such instances exist.”
Consideration for change of conformance statement
This aligns with the above
Proposed resolution
Add proposed text
Proposed action
Update specification, with new text replacing the fourth bullet point in section 9 by:
“Provide descriptions of distributions, if any, of datasets in the catalogue, including at least the mandatory properties specified in section 7.4.1”
Note that there is a conflicting proposal, to make dcat:distribution mandatory for Dataset at http://joinup.ec.europa.eu/release/dcat-application-profile-data-portals-europe-final-draft#comment-14632, under point 1)
The proposed resolution was rejected by the WG at meeting 18 July 2013, see report at https://joinup.ec.europa.eu/document/dcat-application-profile-wg-virtual-meeting-2013-07-18. The WG decided that Distribution should be a Recommended class in section 6.2. In line with this decision, a corresponding change was made in the Conformance section.
The WG resolution has been implemented in draft 0.04 at https://joinup.ec.europa.eu/document/dcat-application-profile-data-portals-europe-draft-final-text.