1. A method comprising: obtaining a plurality of documents, the plurality of documents having corresponding text; performing phrase extraction on the text to obtain a plurality of phrases that appear in the text; filtering out some phrases from the plurality of phrases based on one or more criteria to obtain a subset of the plurality of phrases; mapping individual phrases from the subset of phrases to classes of an ontology model and storing the individual phrases in a knowledge base; analyzing an individual document by applying the classes of the ontology model to occurrences of the phrases in the individual document to infer at least one concept expressed by the individual document; generating output reflecting the at least one concept expressed by the individual document; and performing incremental learning by updating the knowledge base with a new phrase identified in the individual document, wherein at least the phrase extraction is performed using a computing device.