In commercial public cloud the cloud computing enables the model of data service outsourcing. In this paper, the authors define and solve the problem of ranked keyword search over cloud data. Ranked search greatly enhances system usability by enabling search result relevance ranking instead of sending undifferentiated results and further ensures the file retrieval accuracy. They explore the statistical measure approach i.e. relevance score, from information retrieval with focus on ranking and several components of an information retrieval system to build a searchable index.