JRDF Graphs
JRDF graphs are made up of triples (RDF statements). JRDF graphs can also represent parts of other JRDF graphs (known as subgraphs). JRDF graphs can create graph elements and be queried using triples.
The elements (classes) that make up a JRDF graph are as follows:
- Triples
- Nodes
- SubjectNodes
- PredicateNodes
- ObjectNodes
- URIReferences
- BlankNodes
- Literals
The following diagram shows the relationships between the different elements.
JRDF graph elements are created using a GraphElementFactory.
Triples
Triples are made up of three nodes, a SubjectNode, PredicateNode and ObjectNode, representing an RDF statement.
SubjectNodes
A SubjectNode represents an RDF resource (that is, the subject you are describing) and can be either a URIReference or BlankNode. A Literal cannot be a SubjectNode.
PredicateNodes
A PredicateNode represents a property (that is, a characteristic or attribute) of a resource. A PredicateNode can only be a URIReference. A PredicateNode describes the relationship between a SubjectNode and an ObjectNode and cannot be a BlankNode or a Literal.
ObjectNodes
An ObjectNode represents the value of a property. ObjectNodes can be either URIReferences, BlankNodes or Literals.
URIReferences
A URIReference combines a URI (Uniform Resource Identifier) and an optional fragment identifier to identify or represent a SubjectNode, PredicateNode or ObjectNode in a Triple.
BlankNodes
BlankNodes represent intermediate nodes used for representing structured information. For example, an address can be represented either by using a Literal for the whole address, or with a BlankNode as the SubjectNode and subsequent PredicateNodes and ObjectNodes for the different address elements.
Unlike other RDF representations, JRDF does not support labelled BlankNodes.
Literals
A Literal represents a constant value (for example "some literal text"). Literals can optionally have either a datatype URI (for example, http://www.w3.org/2001/XMLSchema#integer) or a language label (for example, en for english), but not both.
GraphElementFactory
Graph elements are created using a GraphElementFactory. A GraphElementFactory creates URIReferences, BlankNodes and Literals that are used to create triples.
Querying a JRDF Graph
Using a triple as a constraint, JRDF graphs can be queried to find all of the triples that match the constraint. Null values are used as wildcards. Querying a JRDF graph using null SubjectNodes, PredicateNodes and ObjectNodes returns all the triples in the graph.
