Raw data files can be hierarchical in structure, consisting of a header record and one or more detail records. Typically, each record contains a field that identifies the record type.

In the raw data file above, the P indicates a header record that contains a patient's ID number. The C indicates a detail record that contains the date of the patient's appointment and the charges that the patient has incurred. This book covers two methods of building a SAS data set from a hierarchical file. You can build a SAS data set from a hierarchical file by creating one observation per detail record, retaining the patient ID from the header record. You can also build a SAS data set from a hierarchical file by creating one observation per header record and combining the information from detail records into summary variables. These are powerful features of SAS that enable complex raw data files to be converted into SAS data sets for statistical analysis.