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Implementation of the Huffman data compression method for a data set involves the development and maintenance of a control table. Each table contains the substitution codes required to compress and expand the data. The tables can also contain information specific to the data set or file. The codes and file information required by the Huffman routines are maintained in File Descriptor Tables (FDTs).
The organization of data within a record can have a significant impact on the algorithm's ability to achieve good compression. The record layout for a data set is described for the Huffman algorithm using the CA Compress Record Definition Language (RDL). The TAILORED algorithm permits you to customize the RDL to achieve maximum compression. The RDL is maintained in the FDT along with the compression and expansion codes and other information.
An FDT can be custom generated for a specific data set or shared by several data sets. Standard FDTs are shared by many data sets. The RDL in a shared FDT must be specified in generic terms since it is used for compressing more than one data set. For more detailed discussions on developing custom RDLs and FDTs, see Record Definition Language and FDT Statement in the
CA Compress Reference Guide.
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