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Re: [dxwg] DataService and DataDistributionService (#432)

From: Simon Cox via GitHub <sysbot+gh@w3.org>
Date: Sun, 13 Jan 2019 08:41:05 +0000
To: public-dxwg-wg@w3.org
Message-ID: <issue_comment.created-453812054-1547368864-sysbot+gh@w3.org>
@agreiner wrote
> Maybe the problem is that we don't come out and say there that a DataDistributionService is a type of DataService, which leaves the reader initially trying to differentiate them since they sound similar.

Right. Figure 1 shows that `DataDiscoveryService` is a subclass of `DataDistributionService` which is a subclass of `DataService`, but this was not clear in the accompanying text. I've attempted to remedy that now - see https://rawgit.com/w3c/dxwg/dcat-issue649-simon/dcat/index.html#dcat-scope again. 

> DiscoveryService is the other type of DataService. But, no, it is actually just a specialization of DataDistributionService, though it offers no additional attributes, which makes it seem kind of useless

There is a little more to it. There is an existential qualifier at line 302 in the RDF representation that requires a `dcat:servesDataset` refer to at least one `dcat:Catalog`. See https://github.com/w3c/dxwg/blob/gh-pages/dcat/rdf/dcat.ttl#L302 : 
```
dcat:DiscoveryService
  rdf:type owl:Class ;
  rdfs:label "Discovery Service" ;
  rdfs:subClassOf dcat:DataDistributionService ;
  rdfs:subClassOf [
      rdf:type owl:Restriction ;
      owl:onProperty dcat:servesDataset ;
      owl:someValuesFrom dcat:Catalog ;
    ] ;
.
```

I've updated the Usage note to mention this. 

The motivation for including `DiscoveryService` was becasue it is one of the key services defined by INSPIRE. Nevertheless, this classification can also be achieved using the `dct:type` property, and the existential qualifier mentioned above is a minor detail. So I would not fight too hard if the group preferred to drop it. 

However, it would be a mistake to collapse the hierarchy entirely by dropping `DataService` as this provides the extensibility point for other kinds of data services, such as data-processing and transformation services. I've added a usage note to the definition of `dcat:DataService` pointing this out - https://rawgit.com/w3c/dxwg/dcat-issue649-simon/dcat/index.html#Class:Data_Service . 

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Received on Sunday, 13 January 2019 08:41:07 UTC

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