HASH 编码数据压缩

DATA COMPRESSION WITH HASH CODES

在数据库应用中常要求数据压缩存贮。所采用的压缩技术应当有较小的系统开销和期望的压缩效果。文章给出了一种用数据在hash 表的位置作为其编码来取代组织在文件中的该数据本身,以减少文件的数据存贮量的压缩方法。对于文件的域,满足域长较大并且域值个数小于总记录数,或者域长大于域值的平均长度时这种编码压缩方法有效;压缩的编码/解码成为对hash 表一次查找或直接访问的开销。文章也讨论了该方法作为一种数据库管理系统的数据压缩存贮工具的实现技术,以及编码和解码的算法。

In many database application,data have to be compressed before storing.Data compression techniques with less overhead and better space saving areusually expected.This paper gives a data compression technique by which the size ofa file may be reduced through substituting codes for its field values.The codes are thecorresponding locations of the values in a hash table that is comprised of all values ofthe field.This compression is effective for many applications.The cost of coding/decoding is equal to that an accessing or searching the hash table.The implementa-tion technique as a compression tool in database management system for data storeand the algorithms of coding/decoding are discussed.