Data analysis using online data summarization processing and rule-based data characteristic detection is performed at the time the transaction data is input. Online data input through an input device of a first server is stored into a transaction data memory device. A data summarizing device carries out summarization processing of online data according to stored parameters, and the resultant summary data is stored into a summary data memory device. A data joining device joins the summary data stored in the summary data memory device and the summary data transferred from a second server for the purpose of updating. In the first server, using rules generated by a rule generating device and stored in rule memory device, a detecting device detects characteristics of the summary data. Further, the results of data characteristic detection are sent to a client through.