9. The non-transitory computer readable medium of claim 6 , wherein the second time pattern comprises at least one of a burst pattern, a period pattern, and a steady pattern with respect to the extended keyword.
9. The non-transitory computer readable medium of claim 6 , wherein the second time pattern comprises at least one of a burst pattern, a period pattern, and a steady pattern with respect to the extended keyword. 10. The non-transitory computer readable medium of claim 9 , wherein the time pattern analysis unit is operable to obtain a time interval from the current time to an extended keyword appearance time and a time interval between extended keyword appearance times based on a connection strength between the keyword and the extended keyword, and to obtain the second time pattern from the time intervals using a statistical probability distribution function.