Caching is an important technique to support pervasive Internet access. Cache consistency measures the deviation between the cached data and the source data. In mobile computing environments, especially with ad hoc networks, users are in great need of the flexibility in tuning their consistency requirements, in order to make tradeoffs between the specified cache consistency and the cost incurred. Existing works have used Delta Consistency (DC) and Probabilistic Consistency (PC) which, to some extent, provide the users with such flexibility. In this paper, we propose a general consistency model called Probabilistic Delta Consistency (PDC). PDC covers all existing consistency models including DC and PC, and integrates the flexibility granted by both DC and PC. Thus, PDC enables the users to flexibly specify their consistency requirements in two orthogonal dimensions, namely the deviation in time/value and the ratio of queries gaining the specified consistency. We also propose a consiste...