Skolemising Blank Nodes while Preserving Isomorphism Blank Nodes

Skolemising Blank Nodes while Preserving Isomorphism 丁文韬

Blank Nodes • Blank nodes add theoretical complexity to RDF. • Blank nodes also introduce practical problems when dealing with RDF. BTC– 2012 corpus • a crawl of 8. 4 million RDF documents from the Web • 44. 9% of the documents mentioned at least one blank node, • 25. 9% of the unique RDF terms were blank nodes • 66. 2% of pay-level-domains used blank nodes.

Skolem IRIs •

Skolemising while Preserving Isomorphism • propose a method for producing a canonical labelling of blank nodes in an RDF graph that preserves isomorphism. checking the isomorphism of RDF graphs or identifying groups of isomorphic RDF graphs from a large collection without requiring pair-wise isomorphism checks Skolemising RDF graphs such that the output graphs are equal if and only if the input graphs are isomorphic

A hashing scheme for the blank nodes

A hashing scheme for the blank nodes •

non-trivial automorphisms •

Canonicalising RDF graphs •

Complete Algorithm dividing parts according to the new colouring while maintaining the prior precedence

Evaluation • Experiments were run in a single-threaded manner on an Intel E 52407 Quad-Core 2. 2 GHz machine with 30 GB of heap space. • BTC– 14 dataset: • • 43. 6 million RDF graphs spanning 47, 560 pay-level-domains around 4 billion quadruples about 1. 1 TB uncompressed in N-Quads format

Evaluation • Some difficult synthetic cases from the Bliss benchmark for standard G-I. • A set of Miyazaki graphs known to be a particularly tough case for G-I. The experiments were run on a laptop With 1 GB of heapspace and an Intel I 3 Dual-Core 2. 4 GHz processor. Using Murmur 3 128

References • Aidan Hogan. Skolemising Blank Nodes while Preserving Isomorphism. In WWW, Florence, Italy, May 18– 22, 2015 • http: //www. w 3. org/TR/rdf 11 -concepts/#section-skolemization • http: //aidanhogan. com/skolem/ • http: //www. tcs. hut. fi/Software/bliss/benchmarks/index. shtml

Thanks for listening • Q&A