RDF URI References: There are certain RDF URI references which are not absolute IRIs (e.g. those containing spaces). It is possible to use such RDF URI references in RDF graphs which are combined with RIF rules. However, such URI references cannot be represented in RIF rules and their use in RDF is discouraged.
Well-typed literals: The notion of well-typed literal is stricter than the notion of well-formed constant symbols in RIF, since it considers all datatypes in some conforming datatype map D as well as all RIF-supported symbol spaces, whereas the notion of well formed constant symbol only considers symbols in the set of RIF-supported symbol spaces.
Generalized RDF graphs: Standard RDF graphs, as defined in [RDF-Concepts], do not allow the use of literals in subject and predicate positions and blank nodes in predicate positions. The RDF Core working group has listed two issues questioning the restrictions that literals may not occur in subject and blank nodes may not occur in predicate positions in triples. Anticipating lifting of these restrictions in a possible future version of RDF, we use the more liberal notion of generalized RDF graph. We note that the definitions of interpretations, models, and entailment in the RDF semantics document [RDF-Semantics] also apply to such generalized RDF graphs.
We note that every standard RDF graph is a generalized RDF graph. Therefore, our definition of combinations applies to standard RDF graphs as well. We note also that the notion of generalized RDF graphs is more liberal than the notion of RDF graphs used by SPARQL; generalized RDF graphs additionally allow blank nodes and literals in predicate positions.