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
Composer in the Romantic music era in the 19th century. In the 20th century, composers began to seek employment as professors in universities and conservatories. In the 20th century, composers also earned money from the sales of their works, such sheet music publications of their songs or pieces or as sound recordings of their works. Notes Sources Composer A composer (Latin "compōnō"; literally "one who puts together") is a musician who is an author of music in any form, including vocal music (for a singer or choir), instrumental music, electronic music, and music which combines multiple forms. A composer may create