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Database seminar: Alejandro Mallea

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Blank nodes in RDF

  • Database Seminar
When Jul 04, 2011
from 05:00 PM to 06:00 PM
Where IF 4.31+4.33, Informatics Forum
Contact Name
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Alejandro Mallea



Blank nodes in RDF



We're working on a survey of a particular feature of RDF that has caused long discussions in the Semantic Web community: blank nodes. The main issue with blank nodes is that the original semantics of RDF intended blank nodes to be existential variables in the same way as in classical model theory from mathematical logic. However, evidence suggests that nobody is following this definition, not even SPARQL, which is the standard query language for RDF. Also, there are theoretical implications that make blank nodes undesirable in their original form. For example, deciding entailment of RDF graphs is NP-complete, but the problem becomes tractable for families of graphs with certain structure in their blank nodes (acyclicity in particular, and bounded treewidth in general). In our work, we also cover a bit of what's been done in database theory about representing incomplete information, and how that could be applied in RDF. Finally, we discuss potential alternatives to the current semantics of RDF (deprecation, elimination, Skolemization), each with its own pros and cons.


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