The Gross Domestic Product (GDP) of a country is derived from different sectors of the economy, namely the agricultural sector, the industrial sector, and the service sector. The sectoral composition of an economy refers to the contribution made by each of these sectors. These contributions collectively make up the structural composition of the economy.

It is not necessary that the service sector should always contribute the maximum to the GDP of an economy. The context states that in some countries, growth in agriculture contributes more to GDP growth, while in others, the service sector contributes more. The dominant sector depends on the specific economic conditions of the country.

However, a general trend is observed where, as a nation becomes more prosperous, the proportion of GDP contributed by agriculture declines considerably. For instance, in India, the proportion of GDP contributed by agriculture declined significantly between 1950 and 1990. This suggests that while the composition shifts away from agriculture with development, it does not imply the service sector must be the maximum contributor in all cases.