A Convention for Schemes and Models

N.B. This seems like undiscovered country (please correct me if I'm wrong), so I'm going to poke my head out and see what happens ...

Danbri has suggested that we need some convention that describes the relationship between the URI for a concept-scheme and the URL(s) for the RDF models that contain all the statements describing the scheme and its constituent concepts.

I suggest the following.

The URI of a concept scheme should resolve to a content-negotiable description of just the scheme itself.

So if the URI of my scheme is http://example.org/myscheme then an http client requesting that resource with Content-type=application/rdf+xml should receive something like the following ...

<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:skos="http://www.w3.org/2004/02/skos/core#"
  xmlns:dc="http://purl.org/dc/elements/1.1/"
  xmlns:temp="http://somewhere.org/modelvocab#" >

  <skos:ConceptScheme rdf:about="http://example.org/myscheme">
    <dc:title>My example scheme</dc:title>
    <dc:description>An example concept scheme.</dc:description>
    <skos:hasTopConcept rdf:resource="http://example.org/myscheme/concept/c0345"/>
    <skos:hasTopConcept rdf:resource="http://example.org/myscheme/concept/c2134"/>
    <skos:hasTopConcept rdf:resource="http://example.org/myscheme/concept/c7956"/>
    <skos:hasTopConcept rdf:resource="http://example.org/myscheme/concept/c5342"/>
    <skos:hasTopConcept rdf:resource="http://example.org/myscheme/concept/c5473"/>
    <temp:loadModel>
      <temp:Model>
        <temp:loadFrom rdf:resource="http://example.org/myscheme/concepts.rdf"/>
      </temp:Model>
    </temp:loadModel>
  </skos:ConceptScheme>

</rdf:RDF>

The vital bit here is all the stuff with a temp: namespace prefix. In a nutshell, I'm saying that we need a way of saying that 'The complete set of statements describing concept scheme X can be loaded from the resource with URL Y' . Now I have no idea what the best way to do this is, hence the temp: stuff - hopefully someone can tell me if there is already an RDF vocabulary for describing this sort of thing, and if not, can help me work out the best way to do it, or even if I'm barking up the right tree or not.

But anyway, if we take this as a temporary starting point, there are some potentially quite interesting scenarios.

For example, perhaps you have a multilingual concept scheme, but you don't want to publish the whole thing as a single resource because perhaps some of your users want to download only labels in a specific language. You could describe this as in e.g. (again making this up off the top of my head) ...

<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:skos="http://www.w3.org/2004/02/skos/core#"
  xmlns:dc="http://purl.org/dc/elements/1.1/"
  xmlns:temp="http://somewhere.org/modelvocab#" >

  <skos:ConceptScheme rdf:about="http://example.org/myMultilingualScheme">
    <dc:title>My example multilingual scheme</dc:title>
    <dc:description>An example multilingual concept scheme.</dc:description>
    <skos:hasTopConcept rdf:resource="http://example.org/myMultilingualScheme/concept/c0345"/>
    <skos:hasTopConcept rdf:resource="http://example.org/myMultilingualScheme/concept/c2134"/>
    <skos:hasTopConcept rdf:resource="http://example.org/myMultilingualScheme/concept/c7956"/>
    <skos:hasTopConcept rdf:resource="http://example.org/myMultilingualScheme/concept/c5342"/>
    <skos:hasTopConcept rdf:resource="http://example.org/myMultilingualScheme/concept/c5473"/>
    <temp:loadModel>
      <temp:Model>
        <temp:unionOf rdf:parseType="Collection">
          <temp:Model>
            <rdfs:comment>The model describing the concept backbone.</rdfs:comment>
            <temp:loadFrom rdf:resource="http://example.org/myMultilingualScheme/concepts.rdf"/>
          </temp:Model>
          <temp:Model>
            <rdfs:comment>The model describing english labels and annotations.</rdfs:comment>
            <temp:loadFrom rdf:resource="http://example.org/myMultilingualScheme/labels_en.rdf"/>
          </temp:Model>
          <temp:Model>
            <rdfs:comment>The model describing the french labels and annotations.</rdfs:comment>
            <temp:loadFrom rdf:resource="http://example.org/myMultilingualScheme/labels_fr.rdf"/>
          </temp:Model>
        </temp:unionOf>
      </temp:Model>
    </temp:loadModel>
  </skos:ConceptScheme>

</rdf:RDF>

So I'm starting to think about what you can do if you can describe set-type operations on models.

Another very interesting scenario is this: Let's say you want to build a new concept scheme, but you don't want to build it from scratch. You want to take two pre-existing schemes, include them, define links between them, and perhaps add a few concepts of your own. Again, a union operation allows you to do this, as in e.g. ...

<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:skos="http://www.w3.org/2004/02/skos/core#"
  xmlns:dc="http://purl.org/dc/elements/1.1/"
  xmlns:temp="http://somewhere.org/modelvocab#" >

  <skos:ConceptScheme rdf:about="http://example.org/myCombinedScheme">
    <dc:title>My example combined scheme</dc:title>
    <dc:description>An example of a concept scheme built on two pre-existing schemes.</dc:description>
    <skos:hasTopConcept rdf:resource="http://authority1.org/scheme/concept/c0345"/>
    <skos:hasTopConcept rdf:resource="http://authority1.org/scheme/concept/c2134"/>
    <skos:hasTopConcept rdf:resource="http://authority1.org/scheme/concept/c7956"/>
    <skos:hasTopConcept rdf:resource="http://authority2.org/scheme/concept/c5342"/>
    <skos:hasTopConcept rdf:resource="http://authority2.org/scheme/concept/c5473"/>
    <owl:imports rdf:resource="http://authority1.org/scheme/"/>
    <owl:imports rdf:resource="http://authority2.org/scheme/"/>
    <temp:loadModel>
      <temp:Model>
        <rdfs:comment>A model containing statements linking the two imported schemes, and some extra concepts of my own.</rdfs:comment>
        <temp:loadFrom rdf:resource="http://example.org/myCombinedScheme/additions.rdf"/>
      </temp:Model>
    </temp:loadModel>
  </skos:ConceptScheme>

</rdf:RDF>

... here I'm relying on some implied semantics in relation to the use of owl:imports: that the complete model describing the combined scheme must include all the statements from the imported schemes (i.e. there is an implied union operation).

This scenario can be extended ... let's say you want to take two pre-existing schemes as a starting point for a new scheme, but you don't want to use all of these schemes - you want to throw some bits out. A set type operation can describe this ...

<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:skos="http://www.w3.org/2004/02/skos/core#"
  xmlns:dc="http://purl.org/dc/elements/1.1/"
  xmlns:temp="http://somewhere.org/modelvocab#" >

  <skos:ConceptScheme rdf:about="http://example.org/myCombinedScheme">
    <dc:title>My example combined scheme</dc:title>
    <dc:description>An example of a concept scheme built on two pre-existing schemes.</dc:description>
    <skos:hasTopConcept rdf:resource="http://authority1.org/scheme/concept/c0345"/>
    <skos:hasTopConcept rdf:resource="http://authority1.org/scheme/concept/c2134"/>
    <skos:hasTopConcept rdf:resource="http://authority1.org/scheme/concept/c7956"/>
    <skos:hasTopConcept rdf:resource="http://authority1.org/scheme/concept/c5342"/>
    <skos:hasTopConcept rdf:resource="http://authority1.org/scheme/concept/c5473"/>
    <owl:imports rdf:resource="http://authority1.org/scheme/"/>
    <owl:imports rdf:resource="http://authority2.org/scheme/"/>
    <temp:loadModel>
      <temp:Model>
        <rdfs:comment>A model containing statements linking the two imported schemes, and some extra concepts of my own.</rdfs:comment>
        <temp:loadFrom rdf:resource="http://example.org/myCombinedScheme/additions.rdf"/>
      </temp:Model>
    </temp:loadModel>
    <temp:excludeModel>
      <temp:Model>
        <rdfs:comment>A model containing the statements from the imported schemes that I want to be removed from my combined scheme.</rdfs:comment>
        <temp:loadFrom rdf:resource="http://example.org/myCombinedScheme/exclusions.rdf"/>
      </temp:Model>
    </temp:excludeModel>
  </skos:ConceptScheme>

</rdf:RDF>

Now there may be a much better way of expressing this with an RDF vocabulary, but it's the principle I want to get across.

The other set operation is an intersection but I can't imagine any really important use scenarios for that yet.

So an important question is, if we are interested in describing set operations on RDF models, can we use the OWL set operation vocabulary to do it, or do we have to make up a new one?

So this could all be quite far out, but I hope stimulating :)