The rules for each category define the duration , the frequency , the size , and the construction attributes of each Expo .
Since the creation of the BIE in 1928 , different protocols have governed Expo categories , which are generally split between World Expos and Specialised Expos .
The rules for each category define the duration , the frequency , the size , and the construction attributes of each World Expos .
Since the creation of the BIE in 1928 , different protocols have governed Expo categories , which are generally split between World Expos and Specialised Expos .