Patent ID: 8700489

Claim:
A server apparatus including a processor, the processor comprising: a purchase history information storage portion that stores at least two pieces of purchase history information of at least two purchasers including purchaser identifying information and purchase time information; a trend leader detecting portion including: a directed graph information constituting unit that: reads two or more pieces of purchase history information from the purchase history information storage portion, acquires purchaser identifying information and purchase time information, and constitutes a directed graph information that the two or more pieces of purchaser identifying information are linked in the order of the purchase time according to the two or more pieces of purchase time information; a trend leader degree calculating unit that: calculates a trend leader degree for each piece of purchaser identifying information from the directed graph information, the trend leader degree being information indicating a degree of being a link origin and a degree of being a trend source, and initializes a trend leader degree vector based on the trend leader degree corresponding to each purchaser identifier; a trend follower degree calculating unit which that: calculates a trend follower degree for each piece of purchase identifying information from the directed graph information, the trend follower degree being information indicating a degree of following a link origin and a degree of following a trend, and initializes a trend follower degree vector based on the trend follower degree corresponding to each purchaser identifier; wherein the trend leader degree calculating unit: determines a next trend leader degree vector by using the directed graph information and the trend follower degree vector, judges whether or not an absolute value of a difference between the next trend leader degree vector and the current trend leader degree vector is smaller than a predetermined threshold, and stores the elements of the next trend leader degree vector as the current trend leader degree vector when judged smaller; wherein the trend follower degree calculating unit: determines a next trend follower degree vector by using the directed graph information and the trend leader degree vector, judges whether or not an absolute value of a difference between the next trend follower degree vector and the current trend follower degree vector is smaller than a predetermined threshold, and stores the elements of next trend follower degree vector as the current trend follower degree vector when judged smaller; a recommended product or service acquiring portion that determines a recommended product or service using both the current trend leader degree vector and the current trend follower degree vector; and a recommended product transmitting portion configured to transmit at least one recommended product or service to an information output apparatus.