CODEWITHSUNDEEP
rdfsemantic-webontologyrdfs
Kai
Kai

Reputation: 191

subClassOf and instance of RDF rdfs:Class

In RDFS, all things are instances of rdfs:Resource. All other classes are subclasses of rdfs:Resource. And rdfs:Resource is an instance of rdfs:Class.

My question is: Could any one help explain this paragraph above? I am confused about this subclass and instance and why they have that relationship.

Upvotes: 2

Views: 2334

Answers (1)

Joshua Taylor
Joshua Taylor

Reputation: 85803

There are three parts here:

All things are instances of rdfs:Resource.

Yup, everything is a resource. You, me, the value true, etc. Everything is a resource. Resource is the catch-all class of everything.

All other classes are subclasses of rdfs:Resource.

The word "other" here might be misleading, since rdfs:Resource is an rdfs:Resource too, since every class is a subclass of itself. But yes, every class is a subclass of rdfs:Resource. X is a subclass of Y when being an instance of X implies being an instance of Y. Since everything is an rdfs:Resource, then for any class X, if something is an X, that same thing is also an rdfs:Resource. (In a sense, this is trivial.)

rdfs:Resource is an instance of rdfs:Class.

Yes. Everything that is a class is an instance of rdfs:Class. rdfs:Resource is a class, so it's an instance of rdfs:Class.

If you want to think in terms of triples, the above mean that

  1. For all x, we have the triple: [x rdf:type rdfs:Resource].
  2. For all x, we have the relationship: if [x rdf:type Class] then [x rdfs:subClassOf rdfs:Resource].
  3. We have the triple: [rdfs:Resource rdf:type rdfs:Class].

You don't mention it in the question, but I wonder if this may be confusing because it leads to the situation that we have all of the following:

  • [rdfs:Resource rdf:type rdfs:Class]
  • [rdfs:Class rdf:type rdfs:Resource]
  • [rdfs:Class rdfs:subClassOf rdfs:Resource]

These might look a little bit odd, but looking at their meaning, they all seem acceptable:

  • resource is a class (i.e., rdfs:Resource is the kind of thing that something can be; it makes sense to say "x is an rdfs:Resource").
  • class is a resource (everything's a resource!)
  • every class is a resource (after all, everything's a resource!)

Upvotes: 7

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