Middle Chinese or the Qieyun system (QYS) is the historical variety of Chinese recorded in the Qieyun, a rhyme dictionary first published in 601 and followed by several revised and expanded editions. The Swedish linguist Bernhard Karlgren thought that the dictionary recorded a speech standard of the capital Chang'an of the Sui and Tang dynasties. However, based on the preface of the Qieyun, most scholars now believe that it records a compromise between northern and southern reading and poetic traditions from the late Northern and Southern dynasties period. This composite system contains important information for the reconstruction of the preceding system of Old Chinese phonology.