day-of-year-from-dateTime() function extracts the amount of days (in the year) from a DateTime attribute so it can be used to compare to a value. Values range from 1 to 366 (due to leap years).
This query returns all the logs where the amount of days (in the year) in
DateAttribute is 30 (for example, “2011-01-30”):
//Logging.Log[day-of-year-from-dateTime(DateAttribute) = 30]