There exist two prevailing theories on the origin of the ethnonym ''*Sŕbъ'' (plur. ''*Sŕby''), one from a Proto-Slavic language with an appellative meaning of a "family kinship" and "alliance", while another from an Iranian-Sarmatian language with various meanings. In his work, ''De Administrando Imperio'', Constantine VII Porphyrogenitus suggests that the Serbs originated from White Serbia near Francia. According to the recorded tradition the White Serbs split in two, with the half that became known as the Serbs coming down to settle Byzantine land. From 1815 to 1882 the official name for Serbia was the Principality of Serbia, from 1882 to 1918 it was renamed to the Kingdom of Serbia, later from 1945 to 1963, the official name for Serbia was the People's Republic of Serbia, later renamed the Socialist Republic of Serbia from 1963 to 1990. Since 1990, the official name of the country has been the Republic of Serbia.