A thematic catalog is a list of works, usually by one composer, which includes a detailed description of each work. Some of these descriptions will include the following:
Our print collection of thematic catalogs is clustered in the REF ML134 section of the fourth-floor stacks
The catalog of a composer's works may be arranged in chronological order by opus or work number or by some other method, for example, by medium of performance. Those arranged by medium of performance may be sub-arranged in chronological order or by key.
An opus number is a unique number assigned by a composer or by publishers to some or all of that composer's work or group of works. Works without opus numbers may be designated as WoO (abbreviated from the German "Werke ohne Opuszahl").
Work numbers (or thematic index numbers) are assigned by the person who creates a catalog of a composer's works. Thematic index numbers generally have an alphabetic prefix in the form of an initial or acronym. For example, the "K." in Mozart's thematic index number stands for Ludwig Köchel, the organizer of Mozart's works, and the letters in the thematic index numbers for J. S. Bach's works, "BWV," stand for Bach-Werke-Verzeichnis [Bach Work List], compiled by Wolfgang Schmieder.