11. The method of claim 10 , wherein deciding the topic comprises: constructing at least one topic segment comprising at least one candidate topic using the collected log information; extracting a sentence constituent element for constituting a sentence from each topic segment; deciding a topic for each topic segment based on a frequency of occurrence of a topic according to the extracted sentence constituent element; and selecting one topic segment for a reference time based on the frequency of occurrence of a topic comprised in each topic segment.
11. The method of claim 10 , wherein deciding the topic comprises: constructing at least one topic segment comprising at least one candidate topic using the collected log information; extracting a sentence constituent element for constituting a sentence from each topic segment; deciding a topic for each topic segment based on a frequency of occurrence of a topic according to the extracted sentence constituent element; and selecting one topic segment for a reference time based on the frequency of occurrence of a topic comprised in each topic segment. 12. The method of claim 11 , wherein constructing the topic segment comprises: constructing at least one topic segment using any one reference log information among a plurality of log information; mapping assistant log information to each topic segment based on a time of occurrence of the assistant log information, and when assistant log information mapped to no topic segment exists, constructing a base segment using the assistant log information mapped to no topic segment, wherein the assistant log information represents log information excepting the reference log information among the plurality of log information.