The Language Graph is a linguistic knowledge base containing millions of concepts and over 100 million facts in the form of relations and annotations. It is used extensively by the linguistic algorithms to predict the senses of words, generate paraphrases, etc.
It contains almost all common words, many common multi-word expressions (e.g., nuclear reactor), and millions of named entities (proper nouns or adjectives). The named entities were mined from popular sources such as Wikipedia, MusicBrainz, etc. Where a sense was obtained from an external reference, that information is available and can be used by an application to establish a mapping between the Idilia sense and the matching Wikipedia page (for example).
Applications use the API to discover the sense inventory for a word, smooth a sense to its parents or obtain its classification information, etc. Queries are formulated using a powerful template language. The API is most often used in conjunction with the Sense Analysis or Matching APIs.