Chemistry is typically defined as the science that studies the composition, structure, and transformation of matter. It has been called "the central science" because of the way it is related with all the other sciences. Chemistry bridges the gap between physics and biology; it is a "helper science" in almost many technical disciplines; and it occupies a prominent position in industry between the extraction of raw materials and the manufacture of finished products. Of course, it is chemists who call it this way; other scientists may have different perspectives. Chemistry is also distinguished from some other sciences because it creates its own object of study: chemists can imagine and create new compounds that have never existed in nature, so they are not constrained to what already exists, but only to what can be done.