Character Data Representation Architecture

Appendix B. Conversion Methods

Conversion tables alone do not ensure the transfer or sharing of data objects between different computing environments: the proper selection and use of these tables is essential. Conversion methods, as described in the following sections, are used with the tables found in the CDRA Conversion Resources to ensure that the desired results are obtained. As with the selection of a table, the conversion method that is best for one application may not be appropriate for another.

It is the responsibility of the person designing the conversion method to respect the characteristics and requirements of the input and output data. An appropriate method can be selected based on the encoding schemes (ESs) and string types (STs) of the input and output data. The conversion method models described in the following sections are specifically for coded graphic character strings whose semantics follow the respective ES definitions for the character encodings. Necessary enhancements needed to deal with the following string types are also briefly described:

Conversion methods are not supplied by CDRA, but are described here in the context of use with the conversion tables created and supplied by CDRA.

Figure 54. Use of Conversion Methods

cvtmeth epsbin - convert methods

Figure 54 shows the use of the conversion methods and tables within the overall conversion process. The conversion method first parses the input data string, and if necessary performs any required substring operation. A substring operation may be required if the input data string contains embedded code-extension controls, such as SO/SI controls in EBCDIC-mixed SBCS/DBCS data. The rules for parsing the specified string type should also be followed. The resulting substrings should contain code points that possess similar characteristics -- they are all from the same CS, CP pair identified. Each substring is converted from input code points to output code points using the appropriate conversion table. This table selection is based on the characteristics of the input data and the desired characteristics of the output data including the CS, CP pairs and ESs. Finally, the conversion method assembles the resulting output substrings into the final output string. This process should include the insertion of any code extension control characters that are required by the output ES. Rules for assembling the specified output string type (ST) should also be followed.

Each of the CDRA conversion methods is explained in detail on the following pages.

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