Coding of the professional data allows to organize comparative researches of professional structure and employment of the population in different countries and regions. The historical international standard of classification of occupations (HISCO), published in the late 20th - early 21th century, is based on coding names of the population#s professions and occupations fixed in historical sources. Except the basic professional information HISCO allows to keep additional data on features of a kind of activity. Each stage of coding information from domestic databases has its own specificity and is considered separately.