Data Sources. Give data sources short, descriptive names consisting of only letters and numbers. Two data tables are built for each data source in the Prepare Data dialog. First, an input table (for example, Crash_In) is prepared by selecting cases and fields from an existing data table. Input data fields are analyzed so that you can decide how best to standardize data for linkage purposes. Second, a standard table (for example, Crash) is prepared by applying the standard methods you specify to fields in the input table. Standard data fields are analyzed so that their statistical characteristics can be used in record linkage algorithms. All standard fields have text values, also known as character values or string values.