Double-Byte Character Set Support

Optim™ processes Double-Byte Character Set (DBCS) data and provides DBCS users with all Optim capabilities that are available to Extended Binary Coded Decimal Interchange Code (EBCDIC) users.

Optim DBCS support assumes EBCDIC DBCS data. EBCDIC DBCS requires exactly two bytes for every DBCS character. Optim DBCS support assumes a single DBCS language, including pure DBCS, and Mixed Single-Byte Character Set (SBCS) and DBCS.

In mixed character strings (strings that contain both SBCS and DBCS characters), two special control characters indicate the start and end of a DBCS substring. Shift Out (X'0E') indicates the start and Shift In (X'0F') indicates the end of the DBCS substring.

DB2^® translates all DB2 character data between the internal DB2 table Coded Character Set Identifier (CCSID) and the external application (Optim) CCSID. All data that Optim processes remains in the external Optim CCSID.

Note: To eliminate problems with round-trip character translation, the Optim installer should ensure that the external Optim CCSIDs match the internal DB2 CCSIDs for DBCS data.

Optim Archive and Extract Files preserve the encoding scheme and CCSID. Optim warns users if incompatible CCSIDs could cause problems in storing data. Site and User options (“Allow Mismatched CCSIDs”) indicate the action Optim should take when the CCSID of a source column does not match that of a target column and when the CCSID of the terminal does not match that of the DB2 subsystem.

DBCS Data Types

Optim supports the following DBCS data types. The conversion and mapping rules for the DBCS data types are the same as the corresponding DB2 rules.

GRAPHIC - A fixed-length data type used to store a graphic string, that is, a string consisting of double-byte EBCDIC characters that are not stored with Shift Out and Shift In characters. The maximum length of a GRAPHIC string is 254 bytes.
VARGRAPHIC/LONGVARGRAPHIC - A varying-length data type used to store a variable-length graphic string. The maximum length of a VARGRAPHIC/LONGVARGRAPHIC string is 32704 bytes.
CHAR or CLOB defined with “FOR MIXED DATA” - Used to store mixed data, that is, Multi-byte Character Set (MBCS) data (the MIXED=YES DB2 install option is required). Shift Out and Shift In characters are required to identify the double-byte data in a mixed character string.
DBCLOB - A double-byte character large object. The maximum length of a DBCLOB is 1,073,741,823 DBCS characters.

Functions that Support DBCS Data

Optim supports DBCS data in the following functional areas:

The Optim ISPF interface accepts and displays DBCS data.
The Optim Directory accepts DBCS characters in object names (for example, column names, table names, Access Definition names, Compare Definition names, relationship names). When DBCS characters are used for an object name, they must be enclosed in double quotes.
Keywords, commands, and control statements remain in EBCDIC SBCS. Batch Optim Directory control statements (for example, EXPORT, IMPORT) support DBCS characters.
Access displays and allows entry of DBCS data.
Archive and Extract processes save and restore DBCS data in Archive and Extract Files. (Archive and Extract Files save data in the external (Optim) application CCSIDs.)
Note: To eliminate problems with round-trip character translation, the Optim installer should ensure that the external Optim CCSIDs match the internal DB2 CCSIDs for DBCS data.
Compare supports DBCS data.
Browse/Edit mode presents DBCS data and allows insert and updates. It also supports DBCS data in Selection Criteria and SQL WHERE clauses.
All Column Map functions support DBCS literals and SUBSTR operations with DBCS data.
Optim checks for data type compatibility between source and destination columns during Insert, Restore, and Convert processes.
Functions that display table names, column names, and relationships support DBCS data.
Export/Import and substitution variables support DBCS data.
Process reports accommodate DBCS data.

Definitions

The following definitions explain terms used in this section:

Coded Character Set Identifier (CCSID): A 16-bit number that uniquely identifies a coded representation of graphic characters. It designates an encoding scheme identifier and one or more pairs that consist of a character set identifier and an associated code page identifier.

Double-Byte Character Set (DBCS): A set of characters, which are used by national languages such as Japanese and Chinese, that have more symbols than can be represented by a single byte. Each character is 2 bytes in length.

Graphic String: A string consisting of double-byte EBCDIC characters that are not stored with Shift Out and Shift In characters.

Multi-Byte Character Set (MBCS): A character set that represents single characters with more than a single byte. UTF-8 is an example of an MBCS. Characters in UTF-8 can range from 1 to 4 bytes in DB2.

Single-Byte Character Set (SBCS): A set of characters in which each character is represented by a single byte.