This is a linked open data (LOD) about date and time. "C.E. 2013 May 01" is a date of Gregorian Calendar (Calendar ID: 2.1).
http://datetime.hutime.org/calendar/2.1/date/C.E._2013_May_01
hcal:2.1/date/2456413.5
hcal:2.1/date/C.E._2013_May_01
hcaldate:2456413.5
hcaldate:C.E._2013_May_01