With increment of personal data amount, how to efficiently manage Personal DataSpace(PDS) becomes a serious problem and a hot research topic. In PDS, users often expect to relocate some known items. Therefore how to efficiently identify these known items from a great number of objects becomes an important research issue. To the best of our knowledge, there is no existing works tackling this problem. In this paper, we propose a concept KnownBy to model the basic relationship between data items and users, and take it as the baseline for deciding if an item belongs to PDS. By analyzing user access logs, we mine some rules for identifying known items, and propose efficient methods for marking known items from personal desktop resources. Our experiments validate the effectiveness and efficiency of our methods, which can be integrated into personal information management systems, such as desktop search tools, and etc.