Joseph Haydn was a prolific composer of the classical period. He is regarded as the "father of the symphony" and the "father of the string quartet" for his more than 100 symphonies and almost 70 string quartets. Haydn also produced numerous operas, masses, concertos, piano sonatas and other compositions. Haydn's works were catalogued by Anthony van Hoboken in his Hoboken catalogue. Unlike most other catalogues which sort works chronologically, the Hoboken catalogue sorts by musical genre.