Extracting semantic classes and instances from text

A computer-readable storage device storing instructions that, when executed by data processing apparatus, cause the data processing apparatus to perform operations comprising:

• receiving a collection of text;
• identifying a first collection of instance-class pairs for the collection of text, wherein the first collection of instance-class pairs are identified by applying one or more template patterns to a collection of documents;
• clustering a collection of semantically similar phrases using the collection of text;
• determining, for each class in the first collection of instance-class pairs:
• whether a threshold number of instances within a cluster in the semantically similar phrase clusters are labeled by the class, and
• whether a threshold number of clusters in the semantically similar phrase clusters include at least one instance that is labeled by the class;
• in response to determining that a threshold number of instances within a cluster are labeled by a class and a threshold number of clusters in the semantically similar phrase clusters include at least one instance that is labeled by the class, selecting each instance in the first collection of instance-class pairs that are labeled by the class to be included in a second collection of instance-class pairs;
• and
• storing the second collection of instance-class pairs for use in information retrieval.

A system comprising:

• one or more processors configured to perform operations comprising:
• receiving a collection of text;
• identifying a first collection of instance-class pairs for the collection of text, wherein the first collection of instance-class pairs are identified by applying one or more template patterns to a collection of documents;
• clustering a collection of semantically similar phrases using the collection of text;
• determining, for each class in the first collection of instance-class pairs:
• whether a threshold number of instances within a cluster in the semantically similar phrase clusters are labeled by the class, and
• whether a threshold number of clusters in the semantically similar phrase clusters include at least one instance that is labeled by the class;
• in response to determining that a threshold number of instances within a cluster are labeled by a class and a threshold number of clusters in the semantically similar phrase clusters include at least one instance that is labeled by the class, selecting each instance in the first collection of instance-class pairs that are labeled by the class to be included in a second collection of instance-class pairs;
• and
• storing the second collection of instance-class pairs for use in information retrieval.