A reference work is a compendium of information, usually of a specific type, compiled in a book for ease of reference. That is, the information is intended to be quickly found when needed. Reference works are usually referred to for particular pieces of information, rather than read cover to cover. The writing style used in these works is informative; the authors avoid use of the first person, and emphasize facts. Indexes are commonly provided in many types of reference work. Updated editions are published as needed, in some cases annually.