Predicting lexical answer types in open domain question and answering (QA) systems
In an automated Question Answer (QA) system architecture for automatic open-domain Question Answering, a system, method and computer program product for predicting the Lexical Answer Type (LAT) of a question. The approach is completely unsupervised and is based on a large-scale lexical knowledge base automatically extracted from a Web corpus. This approach for predicting the LAT can be implemented as a specific subtask of a QA process, and/or used for general purpose knowledge acquisition tasks such as frame induction from text.
1. A system for predicting a lexical answer types (LAT) in a question comprising:
a memory storage device including a plurality of syntactic frames;
a processor device operatively connected to said memory storage device and configured to:
receive a question text string;
extract at least one syntactic frame from said question string,
designate, in said syntactic frame, a placeholder for an entity corresponding to a potential lexical answer type; and
query a lexical knowledge database to automatically obtain at least one replacement term for said placeholder of said at least one syntactic frame,
wherein said entity placeholder is a part of a question focus indicating a LAT of the question.
2. The system as claimed in claim 1 , wherein to extract said at least one syntactic frame, said processor device is further programmed to:
decompose said question text string into said at least one syntactic frame, each syntactic frame including a corresponding a focus slot-value pair, each said slot representing a syntactic role identified by a dependency relation.
3. The system as claimed in claim 1 , wherein said processor device is further configured to:
substitute at least one of said replacement terms with a generalized type information term using a database of entity type knowledge.
4. The system as claimed in claim 3 , wherein said entity type knowledge comprises frames having terms with is_a relationships.
5. The system as claimed in claim 3 , wherein to query said lexical knowledge database to obtain said at least one replacement term, said processor device is configured to apply a Generalized Frame Model to obtain said at least one replacement term.
6. The system as claimed in claim 1 , wherein said processor device is further programmed to:
rank said one or more replacement terms; and
select a top-ranked replacement term as an inferred lexical answer type to said question.
7. The system as claimed in claim 1 , wherein said processor device if further configured to:
filter out said replacement terms if said replacement term is not related to the context of said question.
8. The system as claimed in claim 5 , wherein said lexical knowledge database includes frame structures identified from a corpus of text, a frame structure having one or more slots-value pairs, a slot representing a syntactic role identified by a dependency relation, wherein to apply a Generalized Frame Model, said processor device is further configured to:
specify a frame cut comprising a sub-set of frames having non-empty slot-values for a given subset of slot-values pairs;
specify a frame abstraction to determine a desired relationship among selected selected slot values from said given subset of slot-values pairs; and,
generate, from said frame cut, plural frame vectors defining a multi-dimensional vector space from which relationships among selected selected slot values is determined; and,
processing said frame vectors to determine said desired relationship among selected selected slot values as defined by said abstraction.
9. The system as claimed in claim 8 , wherein said desired relationship includes an inferred type of a slot representing one of: a syntactic subject role or syntactic object in corresponding verb and noun phrases.