A method for extracting a relations graph uses an ontology graph in which nodes represent entity classes or concepts and edges represent properties of the classes. A property is associated with a constraint which defines a range of values that can be taken without incurring a cost. Input text in which entity and concept mentions are identified is received. An optimal set of alignments between a subgraph of the ontology graph and the identified mentions is identified by optimizing a function of the costs of the constraints incurred by the alignments and a distance measure computed over the set of alignments. A relations graph is generated, based on the optimal set of alignments. The relations graph represents a linked set of relations instantiating a subgraph of the ontology. The relations graph can include relations involving implicit mentions corresponding to subgraph nodes that are not aligned to any of the concept or entity mentions.
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