Context Associations: an Application-Independent Annotation Method for RDF Knowledge Graphs

Integrating annotations

• Heterogeneous methods
  • Hard to store uniformly
  • Hard to query generically
• Context and data become hard to distinguish
• How do we ensure uniform extraction of
  associated context in Knowledge Graphs

Annotation requirements

• Interoperable: processed using RDF tooling
• Agnostic: can target any set of RDF statements
• Explicit: data and context are explicitly defined
• Immutable: preserves associations under merge
• Recursive: associations can be recursively defined

For a given associated context

<Credential> <primarySubject> <Alice>
<Alice> <employee> <University>
<Credential> <proof> <ProofGraph>

<ProofGraph> {
    _:proof <proofValue> "..."
}
    

Graphs for target boundary

_:data {
    _:data ca:graphName ca:DefaultGraph
    <Credential> <primarySubject> <Alice>
    <Alice> <employee> <University>
    <Credential> <proof> <ProofGraph>
}

<ProofGraph> {
    _:proof <proofValue> "..."
}
    

Anchor triples to define associations

_:data {
    _:data ca:graphName ca:DefaultGraph
    <Credential> <primarySubject> <Alice>
    <Alice> <employee> <University>
    <Credential> <proof> <ProofGraph>
}

<ProofGraph> {
    <ProofGraph> ca:aboutGraph _:data
    _:proof <proofValue> "..."
}

Blank nodes to prevent conflicting merges

_:data {
    _:data ca:graphName ca:DefaultGraph
    <Credential> <primarySubject> <Alice>
    <Alice> <employee> <University>
    <Credential> <proof> <ProofGraph>
}
_:proofGraph {
    _:proofGraph ca:aboutGraph _:data
                 ca:graphName <ProofGraph>
    _:proof <proofValue> "..."
}
    

Context Associations

• Minimal annotation method using named graphs
• Defines a relation between
  • a named graph of target statements
  • a named graph of context statements
• through an anchor triple in the context graph
  • _:contextGraph ca:aboutGraph _:targetGraph

Querying with SPARQL

• Cannot evaluate variable length
  property paths over named graphs
• Cannot create named graphs with
  SPARQL construct
• Resolved with Apache Jena ARQ

Encoding / decoding

• Define organization of graph links
• Method-specific requirement (JSON-LD frames)

• 
  _:g0 {
    <University> <states> _:b0 .
    _:b0 a rdf:Statement .
    _:b0 rdf:subject <Alice> .
    _:b0 rdf:predicate <employee> .
    _:b0 rdf:object <University> .
  }
            

  
  _:g0 {
    _:g0 ca:aboutGraph _:g1 .
    <University> <states> _:graph .
  }
  _:g1 {
    _:g1 ca:encodedFrom ca:reification .
    <Alice> <employee> <University> .
  }
            

Where does this land us

• Interoperable: ~ works with SPARQL, better with ARQ
• Agnostic: ✓ complexity in encoding step
  
• Explicit: ✓ explicit data, context and encoding info
• Immutable: ✓ stable under dataset merge
• Recursive: ✓ requires custom encoding routines