An Event-Driven Approach for Querying Graph-Structured Data Using Natural Language

An ideal way for people to query graph-based knowledge, including triplestores in the semantic web, would be for them to ask questions in a natural language (NL). However, existing NL query interfaces to graph-based data have limited expressive power and cannot accommodate arbitrarilynested quantification (i.e. phrases such as “a gangster who joined every gang”) together with multiple complex prepositional phrases, such as “in a city located in Illinois in 1918 using a set of keys that was stolen from a gangster”. It would appear that the commonly-used “entity-based” triplestores, together with what has become the de-facto approach of converting NL queries to SPARQL queries before being evaluated, hinders the development of expressive NL query processors. The reason is that entity-based triples are not conducive to the development of semantic theories of complex prepositional phrases, and the development of such theories is made considerably more complex when translation to SPARQL has to be taken into account. An alternative approach, which uses “event-based” triplestores, treats (bracketed) English queries as expressions of the lambda calculus which can be evaluated directly with respect to the triplestore. This approach facilitates the development of a formal denotational semantics of English queries which easily accommodates complex prepositional phrases. The approach described here could be used to develop a denotational semantics for a highly-expressive NL query language, and then that semantics could be used to guide the design of an NL query to SPARQL translator, thereby taking advantage of SPARQL optimizations.