2012 年 29 巻 3 号 p. 3_219-3_231
This paper proposes a monitoring method for information retrieval from the sources in large-scale networks, which tries to achieve the maximum gain of user utility with the minimum source observation cost. Generally, information accumulated in a network is being updated every second and the contents which have been downloaded by network users become obsolete as time passes. User utility, which is obtained by the users when they get their target information successfully, declines with the elapsed time from the instant of placing a retrieval request or the content's renewal. Accordingly, the proposed monitoring method adjusts its observation intervals according to the information sources' update intervals considering user utility decrease and monitoring cost caused by the observation of sources. The usefulness of the proposal is confirmed by computer simulations, which illustrate that it is effective especially in the condition that the expense of the observations is neither extremely emphasized nor neglected. In addition, a prototype of the monitoring system which implemented the proposal is developed and some monitoring experiments in the real Internet environment are conducted. The results show that the proposed method seems to be available in the case where the conditions are close to those of the simulations.