6. An apparatus comprising: a memory; and a processor coupled to the memory and configured to: extract a partial character string including a reserved word and a character string immediately previous or subsequent to the reserved word from each of a plurality of pieces of target data such that a plurality of different partial character strings are extracted, the plurality of pieces of target data conforming to a first pattern character string including the reserved word defined by a protocol, detect a number of the pieces of target data that include each different partial character string extracted from the plurality of pieces of target data, specify a first partial character string from the extracted partial character strings, the first partial character string being specified based on the number of pieces of target data that include the first partial character string or a response time of the pieces of target data that include the first partial character string, and create a second pattern character string for classifying the plurality of pieces of target data based on the first pattern character string and the first partial character string, wherein each of the pieces of target data is a message requesting a process from a server, and the processor is configured to specify the first partial character string from the partial character strings based on a response time from a time when the detected message is transmitted to the server and a time when a response comes from the server.
6. An apparatus comprising: a memory; and a processor coupled to the memory and configured to: extract a partial character string including a reserved word and a character string immediately previous or subsequent to the reserved word from each of a plurality of pieces of target data such that a plurality of different partial character strings are extracted, the plurality of pieces of target data conforming to a first pattern character string including the reserved word defined by a protocol, detect a number of the pieces of target data that include each different partial character string extracted from the plurality of pieces of target data, specify a first partial character string from the extracted partial character strings, the first partial character string being specified based on the number of pieces of target data that include the first partial character string or a response time of the pieces of target data that include the first partial character string, and create a second pattern character string for classifying the plurality of pieces of target data based on the first pattern character string and the first partial character string, wherein each of the pieces of target data is a message requesting a process from a server, and the processor is configured to specify the first partial character string from the partial character strings based on a response time from a time when the detected message is transmitted to the server and a time when a response comes from the server. 7. The apparatus according to claim 6 , wherein the processor is configured to: calculate, for each of the messages, a total response time obtained by accumulating response times each from the time when the detected message is transmitted to the server and the time when the response comes from the server, and specify the first partial character string from the partial character strings based on the total response time for each of the messages.