One problem associated with a frequency analysis by itself is that seldom does the nature of data storage or transmission remain static. Thus, the transmission of normal English text at one point in time might have been preceded by the transmission of a FORTRAN program compilation and execution. This type of data is normally heavily oriented toward scientific notation and numeric characters. In addition, the England text could be followed by a COBOL program execution, usually oriented oriented toward alphanumeric characters and such special symbols as dollar signs, commas and decimal points. To maximize compression performance, if sometimes becomes necessary to recognize the changing frequency patterns of data and employ a different compression technique more suitable to the new data structure. In other cases, a simple examination of data will permit the analyst to recognize that the simple compression technique to another technique already unitized will permit additional operational efficiencies. Conversely, if a data analysis process identifies significant variances you will probably want to consider the development of an adaptive data-compression technique similar to those discussed in Chapter4.