Some composers' musical pieces are identified by opus numbers which generally run either in order of composition or in order of publication. Certain composers' works have been definitively cataloged by a given scholar, and in such instances these works can be unambiguously referred to by their thematic catalog abbreviations.

• Bach's works are referred to by their BWV or Bachwerkverzeichnis numbers after the catalogue by Wolfgang Schmieder[?].
• Haydn's works are referred to by their Hob or Hoboken numbers after Anthony van Hoboken's 1957 classification.
• Mozart's works are referred to by their K or Köchel numbers, after Ludwig von Köchel.
• Schubert's works are referred to by their D or Deutsch numbers after Otto Erich Deutsch[?]'s catalogue.
• Vivaldi's works are referred to by their RV or Ryom Verzeichnis numbers after Peter Ryom[?]'s catalogue.