SWI-Prolog -- Manual

Documentation
- Reference manual
- Packages
  - SWI-Prolog Semantic Web Library 3.0
    - Two RDF APIs
      - library(semweb/rdf11): The RDF database
        
        Query the RDF database
        
        Enumerating and testing objects
        
        RDF literals
        
        Accessing RDF graphs
        
        rdf_default_graph/1
        
        rdf_default_graph/2
        
        Modifying the RDF store
        
        Accessing RDF collections

3.1.4 Accessing RDF graphs

[det]rdf_default_graph(-Graph)
[det]rdf_default_graph(-Old, +New): Query/set the notion of the default graph. The notion of the default graph is local to a thread. Threads created inherit the default graph from their creator. See set_prolog_flag/2.