What is occupational structure? How are occupations generally classified?

The distribution of the population according to different types of occupation
is referred to as Occupational Structure.
Occupations are generally classified as:
(i) Primary activities: These include agriculture, animal husbandry, forestry, fishing, mining and quarrying, etc.
(ii) Secondary activities: These include the manufacturing industry, building and construction work, etc.
(iii) Tertiary activities: These include transport, communication, commerce, administration and other services.