Date conversion functions are of type integer. The Gregorian calendar is used in the date conversion functions. The starting date of Monday, January 1, 1601, was chosen to establish a simple relationship between the date and DAY-OF-WEEK; that is, the integer date 1 was a Monday, DAY-OF-WEEK 1.
For example, the statement:
compute DoW =
function rem (function integer-of-date (date-field) , 7)
returns the day of week for a given date, where 0 is Sunday, 1 is Monday, and so on.