YAGO - Neo4j Mapping

YAGO is based on RDF (Resource Description Framework), a family of specifications from the W3C (World Wide Web Consortium). RDF uses (subject, predicate, object) "triples" which map fairly easily to Neo4j's nodes, properties, and relations. However, there are also some significant differences. So, a bit of structural and syntactic mapping may be appropriate.

Direct Mapping

The SPARQL Plugin for Neo4j maps each RDF triple to a Neo4j relation, generating supporting nodes as needed. Subjects and objects become nodes, with value and kind properties, eg:

{ value='joe',                   kind='literal' }

{ value='http://neo4j.org#sara', kind='uri'     }

Predicates become relations, with cp, c, and p properties, eg:

{ cp='U http://neo4j.org U http://neo4j.org#knows',
   c='U http://neo4j.org',
   p='U http://neo4j.org#knows' }

This allows the plugin to support SPARQL in Neo4j, but the encoding doesn't seem very convenient, let alone idiomatic. There are also issues having to do with encoding efficiency, handling of literal types, etc.

Idiomatic Mapping

Let's see if we can create an idiomatic mapping for YAGO that is also convenient and efficient. We'll start with first principles, then suggest accommodations...

  • Any component of a triple may be a unique name (ie, URI).

  • The object component may also be a literal (eg, "joe", "1.85"^^<m>).

  • Most triples that have literals as objects become node properties.

  • The remaining triples generate relations (and supporting nodes).

  • URI prefixes (eg, owl, rdfs) have their own property (ns).

  • The default prefix (yago) is not recorded.

See Syntax for details on handling of concrete syntax and Predicates for a discussion of predicate mapping.

Nodes

To allow Cypher to make numeric comparisons, we remove the metadata from some predicate-based properties (eg, has_height).

( {
  node:             'fred_frobisher',
  has_given_name:   'fred',
  has_height:       1.85,
  ...
} )

Relations

Relations look something like this:

-[ :Has_predecessor ]->

Helpers

In some cases, it may make sense to create helper nodes and/or relations. For example, some kinds of pattern-based date comparisons can be supported by collections of year, month, and day nodes.


This wiki page is maintained by Rich Morin, an independent consultant specializing in software design, development, and documentation. Please feel free to email comments, inquiries, suggestions, etc!

This topic: Projects/YAGO > Neo4j_Mapping
Topic revision: 04 Apr 2016, RichMorin
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