IBM(R)'s Character Data Representation Architecture (CDRA) deals with the differences in string representation and encoding. The Coded Character Set Identifier (CCSID) is a key element of this architecture. A CCSID is a 2-byte (unsigned) binary number that uniquely identifies an encoding scheme and one or more pairs of character sets and code pages.
A CCSID is an attribute of strings, just as length is an attribute of strings. All values of the same string column have the same CCSID.
In each database manager, character conversion involves the use of a CCSID Conversion Selection Table. The Conversion Selection Table contains a list of valid source and target combinations. For each pair of CCSIDs, the Conversion Selection Table contains information used to perform the conversion from one coded character set to the other. This information includes an indication of whether conversion is required. (In some cases, no conversion is necessary even though the strings involved have different CCSIDs.)
Different types of conversions may be supported by the database manager. Round-trip conversions attempt to preserve characters in one CCSID that are not defined in the target CCSID so that if the data is subsequently converted back to the original CCSID, the same original characters result. Enforced subset match conversions do not attempt to preserve such characters. For more information, see IBM's Character Data Representation Architecture (CDRA).
(C) Copyright IBM Corporation 1992, 2006. All Rights Reserved.