Opus number developed other catalogue-number systems; among them the "Bach-Werke-Verzeichnis" (BWV-number), and the "Köchel-Verzeichnis" (K- and KV -numbers) with which are organised the works of Johann Sebastian Bach and Wolfgang Amadeus Mozart, respectively. In the classical period, the Latin word "opus" ("work", "labour") was used to identify, list, and catalogue a work of art. By the 15th and 16th centuries, the word "opus" was used by Italian composers to denote a specific musical composition, and by German composers for collections of music. In compositional practise, numbering musical works in chronological order dates from 17th century Italy, especially Venice. In common usage, the
Köchel catalogue three revised editions of the catalogue. Subsequent editions – especially the third edition (K) by Alfred Einstein (1937), and the sixth edition (K) by Franz Giegling, , and Alexander Weinmann (1964) – have reflected attempts to arrange the growing list of works in a more accurate chronological order, according to various levels of scholarship. A major shortcoming of K was that there was no room to expand the strictly sequential numbering in the main catalogue to allow for any new discoveries or further reassessment of existing works. For the 1937 edition (K) Einstein (following the analyses of Théodore de Wyzewa