1. A computer-readable storage medium storing a service process analysis program for analyzing service process status in a network system including a plurality of servers, the service process analysis program causing a computer to function as an apparatus comprising: (a) a message collector collecting messages exchanged in the network system; (b) a message parser parsing the collected messages; (c) a message record memory storing records of the parsed messages; (d) a definite transaction finder that identifies definite transactions by extracting, from the records stored in the message record memory, a combination of messages having unique and definite call dependency therebetween, besides satisfying a predetermined requirement concerning the call dependency; (e) a transaction candidate builder that selects each unsettled message included in neither the definite transactions nor previously estimated transactions, extracts a plurality of combinations of messages including the unsettled message selected, as well as satisfying the predetermined requirement, and produces one or more transaction candidates from the plurality of combinations of messages; (f) a candidate evaluator that evaluates likelihood of each of the transaction candidates, based on how many transactions of the same class have been identified as the definite transactions or estimated transactions; (g) a transaction estimator that produces another estimated transaction by selecting one of the transaction candidates based on the likelihood thereof; and (h) a result output unit that outputs the definite transactions and estimated transactions as an analysis result.