A question answering system is an advanced form of an information retrieval system. It can answer, by using a natural language accurately and briefly, questions that users ask in the natural language.
A Resource Description Framework (RDF) repository is a basis for implementing the question answering system. The RDF repository, also referred to as a knowledge base, generally includes a large quantity of triplets that assist a computer in recognition and understanding. Each triplet is expressed in the form of a subject, a predicate, and an object, for example, a subject “An Actor Prepares”, a predicate “category”, and an object “book”. A current question answering system mainly includes two phases: a question understanding phase and a query executing phase. In the question understanding phase, the question answering system first translates a natural language question N into an SPARQLs query sentence, where the SPARQLs is a language for executing query in the RDF repository; and then, in the query executing phase, the question answering system inputs the SPARQLs query sentence to an SPARQLs search engine to find an answer to the natural language question N in the RDF repository.