An English Language Question Answering System
for a Large Relational Database
By typing requests in English, casual users
will be able to obtain explicit answers from a 
large relational database of aircraft flight and maintenance
data using a system called PLANES.  The 
design and implementation of this system is described and
illustrated with detailed examples of the operation 
of system components and examples of overall system
operation.  The language processing portion of the 
system uses a number of augmented transition networks,
each of which matches phrases with a specific 
meaning, along with context registers (his tory keepers)
and concept case frames; these are used for judging 
meaningfulness of questions, generating dialogue for clarifying
partially understood questions, and resolving 
ellipsis and pronoun reference problems.  Other system components
construct a formal query for the relational 
database, and optimize the order of searching relations.
 Methods are discussed for handling vague or 
complex questions and for providing browsing ability.
 Also included are discussions of important issues 
in programming natural language systems for limited domains,
and the relationship of this system to others. 
CACM July, 1978
Waltz, D.L.
