ODMF2 — Design of RDF metamodel for rdf:Statement, triple, and graph controversial

Design of RDF metamodel for rdf:Statement, triple, and graph controversial in semantic web community. In November-December 2007, there were discussions of the ODM metamodels for RDF and OWL
within the OWL working group of the W3C. It became clear from these discussions that key OWL
and RDF experts were surprised and not particularly happy with how ODM modeled the RDF data
model and reification vocabulary. These portions of the RDF specification describe the fundamental
data model for RDF assertions: Triple with subject, predicate and object properties; Graphs for
collecting triples as sets of assertions; and a reification vocabulary enabling assertions about triples
themselves. Pragmatic design decisions were made for the ODM metamodel which merged support
for triples and the reification vocabulary into a single class, Statement, and merged support for a
non-standard extension for RDF, named graphs, with graph.
Unfortunately, the reification vocabulary
for RDF has proved problematic and controversial, and because these aspects are key to the semantics
of RDF, some are very sensitive about how they are modeled.
To encourage better acceptance of ODM in the semantic web community the RDF metamodel should
be changed to correspond with expectations of SemWeb experts. Triples, Statements, Graphs and
Named Graphs should all be modeled with separate constructs with non-normative and non-standard
elements noted. The OWL Ontology model which uses these constructs should be modified to use the
fundamental rdf forms: triple and graph, and should do this in a way consistent with the RDF
specifications, e.g., RDF triples in a graph are considered unordered (a set).

Factor the Statements diagram in Figure 10.2 in RDFBase into 3 diagrams: Graph Data Model, Reification, and Graphs. This separates rdf triples from statements about them and creates a separate construct for Named Graph since it is not a part of the current rdf specification. The diagram for rdf:statements is now called Reification (rdfs calls this the reification vocabulary), the Graph Data Model diagram depicts triples, and the Graphs diagram depicts RDF graphs and named graphs. New subsections in RDFBase will be added for RDF Reification and Graphs: Reification after the Literals section and Graphs after Reification.
Places in odm metamodels which extended or otherwise referred to statements are changed to refer to triples. This includes the Documents model in the RDFWeb package and the Ontology model in OWLBase.
Changes include:
§ Changing section 10.2 from describing RDF Statements to describing Triples.
§ Revising figure 10.2 to describe triples, moving RDF Graph to 10.5, eliminating Reification kind, and introducing a supertype which is a complete and disjoint covering for URIReferenceNode, BlankNode, and RDFLiteral called Node for RDFSubject and RDFObject roles from Triple.
§ Adding a new section 10.4 called RDF Statements to describe the RDF reification vocabulary. Including a diagram describing Statements and its relationship to Triples.
§ Adding a new section 10.5 called Graphs describing rdf graphs and named triples. This includes a Graphs diagram depicting RDF Graphs and Named Graphs as separate classes and including associations on named graphs to for equivalentGraphs and subGraphs per the seminal named graphs reference.
§ Revising Documents and Namespaces in the RDFWeb package to refer to triples instead of statements and revising the Documents diagram accordingly.
§ Revising OWL Ontology section and diagram in the OWLBase package to refer to triples instead of statements and to eliminate

attribute for sets of triples.