One common kind of relatedness between words is if they belong to the same semantic field. A semantic field is a set of words which cover a particular semantic semantic field domain and bear structured relations with each other. For example, words might be related by being in the semantic field of hospitals (surgeon, scalpel, nurse, anesthetic, hospital), restaurants (waiter, menu, plate, food, chef), or houses (door, roof, kitchen, family, bed). Semantic fields are also related to topic models, like Latent topic models Dirichlet Allocation, LDA, which apply unsupervised learning on large sets of texts to induce sets of associated words from text. Semantic fields and topic models are very useful tools for discovering topical structure in documents.