상대적인 시간정보 표현을 위한 schema 설계 about slotminer HOT 2 OPEN

attributes ::= type text extent calendar [year] [month] [day] [week] [week_day] [mod] 
type ::= 'DATE' | 'TIME' | 'DURATION'
text ::= CDATA
extent ::= [(begin, end), ...]
begin ::= CDATA {begin ::= <integer>}
end ::= CDATA {end ::= <integer>}
calendar ::= 'GREGORIAN' | 'LUNAR' | 'JULIAN'
year ::= mark CDATA
month ::= mark CDATA
day ::= mark CDATA
hour ::= mark CDATA
minute ::= mark CDATA
second ::= mark CDATA
week ::= mark CDATA
week_day ::= 0 | 1 | 2 | 3 | 4 | 5 | 6
mark ::= 'P' | '+' | '-' | '_' (Note: '_'는 '기원전' 표현 전용)
mod ::= 'START' | 'MID' | 'END' | 'START_MID' | 'MID_END'