43. A combination for use in a computer system that receives user requests to compress uninterrupted byte strings of data sets recorded into storage locations of the computer system and that maintains data catalogs containing information identifying the format of each data set and its storage location, the data sets comprising records of data and assuming either a closed status in which the data set cannot be accessed or an open status in which the data set is subject to access commands, the combination comprising: (a) a library of dictionary segments that are adapted for use by the computer system to create a Ziv-Lempel tree for a data compression process; (b) an interrogation processor that initiates scanning of a plurality of the data set records during an initial recordation of the records to the storage locations and generates predetermined data characteristic statistics relating to the scanned records for selecting dictionary segments from the library according to the generated data characteristic statistics and combining the selected dictionary segments to form a system-built dictionary.
43. A combination for use in a computer system that receives user requests to compress uninterrupted byte strings of data sets recorded into storage locations of the computer system and that maintains data catalogs containing information identifying the format of each data set and its storage location, the data sets comprising records of data and assuming either a closed status in which the data set cannot be accessed or an open status in which the data set is subject to access commands, the combination comprising: (a) a library of dictionary segments that are adapted for use by the computer system to create a Ziv-Lempel tree for a data compression process; (b) an interrogation processor that initiates scanning of a plurality of the data set records during an initial recordation of the records to the storage locations and generates predetermined data characteristic statistics relating to the scanned records for selecting dictionary segments from the library according to the generated data characteristic statistics and combining the selected dictionary segments to form a system-built dictionary. 45. A combination as defined in claim 43, wherein the interrogation processor completes a stabilization procedure by repeatedly performing the steps of selecting a current record block for scanning and generating a current set of the data characteristic statistics, selecting a new record block, different from the current block, for scanning and generating a new set of the data characteristic statistics, and comparing like statistics of the current set of data characteristic statistics and the new set of data characteristic statistics, until the difference between the like statistics is below a predetermined stabilization threshold value or the number of scanned record blocks equals a predetermined scanning limit value, and thereupon storing the new block in an interrogation buffer and storing the set of new data characteristic statistics in the memory if the entropy value is below a predetermined entropy threshold value; wherein the size of each new record block is greater than the size of the current record block.