A system, a method and a computer readable storage medium for pre-processing data collected from one or more data sources more accurately summarize data. During the pre-processing, multiple raw data are summarized into a pre-processed datum. By using the pre-processed data entries, more accurate trend data may be generated. Alternatively, data entries are indexed and selectively retrieved based on indices. Decimation of data points are performed based on the indices without retrieving all the data sets from the database, reducing the data access time for returning a query result. Additional data sets may also be retrieved efficiently from the database using the indices.