An essential feature of AppleScript is coercion. Coercing a quantity into a given class is changing its class into a new one. To perform coercion use the as preposition:

set the_year to "2003" as integer

will store the integer number 2003 into the_year, coercing the string "2003" into an integer.

Whenever implicitly implied, AppleScript performs automatic coercions.

set the_year to 0 + "2003"

will store the integer number 2003 into the_year as well.

AppleScript is rather versatile concerning data types: keep in mind that a given AppleScript operator or function may support several data types in input.