This Annex to the Guide to the Use of Character Sets in Europe provides more detailed information about 8-bit character set standards than is found in the main body of the Guide. Annex B deals in more detail with the Universal Multi-octet Coded Character Set (UCS) specified in ISO/IEC 10646-1.
The need to represent characters by bit combinations (binary numbers) is central to the storage and processing of data by computer systems and the interchange of data between such systems. This annex gives guidance on the many standards and other specifications which have been developed to address the issues that arise from this need up and until the advent of the multi-octet code structure embodied in ISO/IEC 10646-1:1993.
The requirement for compatibility between newer and older equipment has led to the standards of the present day containing legacies from decisions taken many years ago. The reasons behind those decisions are often no longer relevant and their present day legacies may appear merely as unnecessary oddities and complexities. This annex includes some historical background which however is not necessary for an understanding of the remainder of the text.
As work on character sets has developed, there has been a gradual refinement of the concepts involved. This has led to character set standards and other literature making use of technical terms that can be a barrier to the reader. It may be helpful to read section 1.2, Concepts and terminology, before exploring the remaining sections in detail.
This gradual evolution of character set standards has led to technical innovations designed to increase the capabilites of coded character sets while remaining backwardly compatible with what has gone before. Within this evolved framework it is now possible to support a wide range of languages. The wider the range that it is required to support simultaneously, however, the more complex is the technical innovation required. For further information see section 3.1, Language support.
Not all the technical innovations are compatible with all the ways that character data may be used by applications. Section 5.1, Application Environments, provides guidance on these limitations.
Other sections provide greater detail on particular issues.