Quad class final

Represents an immutable RDF quad with graph context

An RDF quad extends the triple model (subject, predicate, object) with a fourth component that specifies the graph containing the statement. This enables:

• Context tracking: Know which graph contains each statement
• Provenance management: Track the source or context of RDF data
• Dataset operations: Work with multi-graph RDF datasets efficiently
• N-Quads support: Direct compatibility with quad-based serialization

The graph component can be null to indicate the default graph, following RDF 1.1 Dataset semantics where every dataset has exactly one default graph and zero or more named graphs.

Design Principles

• Standard Parameter Order: Uses (S, P, O, G) order consistent with other RDF libraries
• Immutability: All components are final, ensuring thread safety
• Null Graph Handling: Null graph name represents the default graph
• Triple Compatibility: Easy bidirectional conversion with Triple class

Example:

// Create quad with named graph
final namedQuad = Quad(
  IriTerm('http://example.org/alice'),
  IriTerm('http://xmlns.com/foaf/0.1/name'),
  LiteralTerm.string('Alice'),
  IriTerm('http://example.org/graphs/people')
);

// Create quad in default graph
final defaultQuad = Quad(alice, foaf.email, aliceEmail);