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ISO 8859

ISO 8859, également appelé plus formellement ISO/IEC 8859, est un standard commun de l'ISO et de l'IEC d'encodage de caractères (character encoding) sur 8 bits pour le traitement informatique du texte. Le standard est divisé en parties numérotées publiées séparément, telles que ISO/IEC 8859-1, ISO/IEC 8859-2, etc., chacune pouvant être référencée de façon informelle en tant que standard en tant que tel. Le standard comprend actuellement 15 parties.

Introduction

Alors que les 96 caractères imprimables ASCII sont suffisants pour échanger des informations en anglais courant, la plupart des autres langues utilisant l'alphabet romain ont besoin de symboles additionnels non couverts par l'ASCII, tels que ß (allemand), å (suédois et d'autres langues nordiques). ISO 8859 a cherché à remédier à ce problème en utilisant le huitième bit, alors inutilisé en ASCII, pour donner de la place à 128 caractères supplémentaires. Cependant, plus de caractères étaient nécessaires pour parvenir à cette fin par rapport à ce qu'aurait permis un unique encodage de caractères sur 8 bits, aussi plusieurs tables de correspondances ont été développées, en incluant au moins 10 tables pour couvrir uniquement le script latin avec les langues modernes officielles.

Le standard ISO 8859-n n'est pas totalement identique aux encodages de caractères bien connus ISO-8859-n approuvés par l'IANA pour l'utilisation sur l'Internet. Au-delà du trait d'union ajouté présent dans le nom approuvé par l'IANA, les encodages diffèrent de sorte que chaque partie du standard ISO assigne, au maximum, 191 caractères dans les étendues d'octets 32 à 126 et 160 à 255, alors que l'encodage de caractère correspondant approuvé par l'IANA fusionne ces tables de correspondances avec le jeu de contrôle C0 (caractères de contrôles positionnés aux octets de 0 à 31) et le jeu de contrôle C1 (caractères de contrôles positionnés aux octets de 127 à 159), ce qui conduit à une table de caractères 8 bits complète, avec la plupart, sinon la totalité, des valeurs d'octets assignées.

Caractères

Le standard ISO 8859 est conçu pour l'échange fiable d'informations, et non pour la typographie; le standard omet des symboles nécessaires pour la typographie de haute qualité, telles que les ligatures optionnelles, les marques de citation incurvées, les tirets, etc. de ce fait, les systèmes de composition avancés utilisent souvent des extensions propriétaires ou pointilleuses au-delà des standards ASCII et ISO 8859, ou utilisent plutôt Unicode.

As a rule of thumb, if a character or symbol was not already part of a widely used data-processing character set and was also not usually provided on typewriter keyboards for a national language, it didn't get in. Hence the directional double quotation marks « and » used for some European languages were included, but not the directional double quotation marks “ and ” used for English and some other languages. French didn't get its œ and Œ ligatures because French speakers had not previously needed them enough to demand them on their keyboards; nor did it get Ÿ, because this character is only used in French in all caps text. These characters were, however, included later with ISO 8859-15, which also introduced the new Euro character €. Likewise Dutch did not get the 'ij' and 'IJ' letters, because Dutch speakers had gotten used to typing these as two letters instead. Romanian did not initially get its 'Ș/ș' and 'Ț/ț' letters, because these letters were initially unified with 'Ş/ş' and 'Ţ/ţ' by the Unicode Consortium, considering the shapes with comma beneath to be glyph variants of the shapes with cedilla. However, the letters with explicit comma below were later added to the Unicode standard and are also in ISO 8859-16.

Most of the ISO 8859 encodings provide diacritic marks required for various European languages. Others provide non-Roman alphabets: Greek, Cyrillic, Hebrew, Arabic and Thai. However, the standard makes no provision for the scripts of East Asian languages (CJK), as their ideographic writing systems require many thousands of code points. Although it uses Latin based characters, Vietnamese does not fit into 96 positions either; Japanese syllabic Kana scripts, on the other hand, might, but like several other alphabets of the world isn't encoded.

Les parties du standard ISO 8859

ISO 8859 est constitué à ce jour des parties suivantes:

• ISO 8859-1 (latin-1 or européen occidental) — probablement la partie la plus largement utilisée de ISO 8859, couvrant la plupart des langues européennes occidentales : allemand, anglais, basque, catalan, danois, écossais, espagnol, féroïen, finois (partiellement²), français (partiellement²), islandais, irlandais, italien, néerlandais (partiellement¹), norvégien, portugais, rhéto-roman et suédois, certaines langues européennes sud-orientales albanais, de même que des langues africaines (afrikaaner et swahili. Le symbole manquant Euro et la capitale Ÿ sont dans la version révisée ISO 8859-15 (latin-9). Le jeu de caractères correspondant ISO-8859-1 approuvé par l'IANA est l'encodage par défaut des anciens documents HTML ou des documents transmis par messages MIME, tels que les réponses HTTP quand le type de média du document est « text » (par exemple les documents « text/html »).
• ISO 8859-2 (latin-2 or européen central) — supporte les langues d'Europe Centrale ou de l'Est basées sur un alphabet romain, y compris le polonais, le tchèque, le slovaque, le [langue slovène|slovène et le hongrois. Le symbole Euro manquant est présent dans la version ISO 8859-16.
• ISO 8859-3 (latin-3 or européen du Sud) — turc, maltais, et Espéranto ; largement supplanté par ISO 8859-9 pour le turc, et Unicode pour l'Espéranto.
• ISO 8859-4 (latin-4 or européen du Nord) — estonien, letton, lithuanien, groenlandais, and sami.
• ISO 8859-5 (cyrillique) — Couvre la plupart des langues slaves utilisant un alphabet cyrillique, y compris le bélarusse, le bulgare, le macédonien, le russe, le serbe et l'ukrainien.

s*ISO 8859-6 (arabe) — Covers the most common Arabic glyphs, although not nearly all of them.

• ISO 8859-7 (grec) — Covers the modern Greek language (monotonic orthography). Can also be used for Ancient Greek written without accents or in monotonic orthography, but lacks the diacritics for polytonic orthography. These were introduced with Unicode.
• ISO 8859-8 (hébreu) — Covers the modern Hebrew alphabet as used in Israel. In practice two different encodings exist, logical and visual.
• ISO 8859-9 (latin-5 or turc) — Largely the same as ISO 8859-1, replacing the rarely used Icelandic letters with Turkish ones. It is also used for Kurdish.
• ISO 8859-10 (latin-6 or nordique) — a rearrangement of Latin-4. Considered more useful for Nordic languages. Baltic languages use Latin-4 more.
• ISO 8859-11 (langue thaïe, thaï) — Contains most glyphs needed for the Thai language.
• ISO 8859-12 — was supposed to be Latin-7 and cover Celtic, but this draft was rejected. Numbering continued with -13.
• ISO 8859-13 (latin-7 or balte) — Added some glyphs for Baltic languages which were missing from Latin-4 and Latin-6.
• ISO 8859-14 (latin-8 or celtique) — Mostly a rearrangement of the ISO 8859-12 draft. Covers Celtic languages such as Gaelic and the Breton language.
• ISO 8859-15 (latin-9 ou parfois de façon impropre latin-0) — a revision of 8859-1 that removes some little-used symbols, replacing them with the Euro symbol € and the letters Š, š, Ž, ž, Œ, œ, and Ÿ, which completes the coverage of French and Finnish.
• ISO 8859-16 (latin-10 or européen du Sud-Est) — Intended for Albanian, Croatian, Hungarian, Italian, Polish, Romanian and Slovenian, but also Finnish, French, German and Irish Gaelic (new orthography). The focus lies more on letters than symbols. The currency sign is replaced with the Euro symbol.

¹: only the IJ/ij (Dutch Y) is missing, which can be represented as IJ
²: missing characters are in ISO 8859-15

Each part of ISO 8859 is designed to support languages that often borrow from each other, so the characters needed by each language are usually accommodated by a single part. However, there are some characters and language combinations that are not accommodated without transcriptions. Efforts were made to make conversions as smooth as possible. For example, German has all its seven special chars at the same positions in all Latin variants (1-4, 9-10, 13-16), and in many positions the characters only differ in the diacritics between the sets. In particular, variants 1-4 were designed jointly, and have the property that every encoded character appears either at a given position or not at all.

Table

At position 0xA0 there's always the non breaking space and 0xAD is mostly the soft hyphen, which only shows at line breaks. Other empty fields are either unassigned or the system used isn't able to display them.

Relations avec Unicode et UCS

Since 1991, the Unicode Consortium has been working with ISO to develop the Unicode Standard and ISO/IEC 10646: the Universal Character Set (UCS) in tandem. This pair of standards was created to unify the ISO 8859 character repertoire, among others, by assigning each character, initially, to a 16-bit code value, with some code values left unassigned. Over time, their models adapted to map characters to abstract numeric code points rather than fixed bit-width values, so that more code points and encoding methods could be supported.

Unicode and ISO/IEC 10646 currently assign about 100,000 characters to a code space consisting of over a million code points, and they define several standard encodings that are capable of representing every available code point. The standard encodings of Unicode and the UCS use sequences of one to four 8-bit code values (UTF-8), sequences of one or two 16-bit code values (UTF-16), or one 32-bit code value (UTF-32 or UCS-4). There is also an older encoding that uses one 16-bit code value (UCS-2), capable of representing one-seventeenth of the available code points. Of these encoding forms, only UTF-8's byte sequences are in a fixed order; the others are subject to platform-dependent byte ordering issues that may be addressed via special codes or indicated via out-of-band means.

Newer editions of ISO 8859 express characters in terms of their Unicode/UCS names and the U+nnnn notation, effectively causing each part of ISO 8859 to be a Unicode/UCS character encoding scheme that maps a very small subset of the UCS to single 8-bit bytes. The first 256 characters in Unicode and the UCS are identical to those in ISO-8859-1.

ISO 8859 was favored throughout the 1990s, having the advantages of being well-established and more easily implemented in software: the equation of one byte to one character is simple and adequate for most single-language applications, and there are no combining characters or variant forms.

As the relative cost, in computing resources, of using more than one byte per character began to diminish, programming languages and operating systems added native support for Unicode alongside their system of code pages. As Unicode-enabled operating systems became more widespread, ISO 8859 and other legacy encodings became less popular. While remnants of ISO 8859 and single-byte character models remain entrenched in many operating systems, programming languages, data storage systems, networking applications, display hardware, and end-user application software, most modern computing applications use Unicode internally, and rely on conversion tables to map to and from the simpler encodings, when necessary.

État de développement

The ISO/IEC 8859 standard was maintained by ISO/IEC Joint Technical Committee 1, Subcommittee 2, Working Group 3 (ISO/IEC JTC 1/SC 2/WG 3). In June 2004, WG 3 disbanded, and maintenance duties were transferred to SC 2. The standard is not currently being updated, as the Subcommittee's only remaining Working Group, WG 2, is concentrating on development of ISO/IEC 10646.

Références

• Published versions of each part of ISO/IEC 8859 are available, for a fee, from theISO catalogue site and from the ANSI eStandards Store .

• PDF versions of the final drafts of some parts of ISO/IEC 8859 as submitted for review & publication by ISO/IEC JTC 1/SC 2/WG 3 are available at the WG 3 web site :
  • ISO/IEC 8859-1:1998 - 8-bit single-byte coded graphic character sets, Part 1: Latin alphabet No. 1 (draft dated February 12, 1998, published April 15, 1998)
  • ISO/IEC 8859-4:1998 - 8-bit single-byte coded graphic character sets, Part 4: Latin alphabet No. 4 (draft dated February 12, 1998, published July 1, 1998)
  • ISO/IEC 8859-7:1999 - 8-bit single-byte coded graphic character sets, Part 7: Latin/Greek alphabet (draft dated June 10, 1999; superseded by ISO/IEC 8859-7:2003, published October 10, 2003)
  • ISO/IEC 8859-10:1998 - 8-bit single-byte coded graphic character sets, Part 10: Latin alphabet No. 6 (draft dated February 12, 1998, published July 15, 1998)
  • ISO/IEC 8859-11:1999 - 8-bit single-byte coded graphic character sets, Part 11: Latin/Thai character set (draft dated June 22, 1999; superseded by ISO/IEC 8859-11:2001, published Dec 15, 2001)
  • ISO/IEC 8859-13:1998 - 8-bit single-byte coded graphic character sets, Part 13: Latin alphabet No. 7 (draft dated April 15, 1998, published October 15, 1998)
  • ISO/IEC 8859-15:1998 - 8-bit single-byte coded graphic character sets, Part 15: Latin alphabet No. 9 (draft dated August 1, 1997; superseded by ISO/IEC 8859-15:1999, published March 15, 1999)
  • ISO/IEC 8859-16:2000 - 8-bit single-byte coded graphic character sets, Part 16: Latin alphabet No. 10 (draft dated November 15, 1999; superseded by ISO/IEC 8859-16:2001, published July 15, 2001)

• ECMA standards, which in intent correspond exactly to the ISO/IEC 8859 character set standards, can be found at:
  • Standard ECMA-94 : 8-Bit Single Byte Coded Graphic Character Sets - Latin Alphabets No. 1 to No. 4 2nd edition (June 1986)
  • Standard ECMA-113 : 8-Bit Single-Byte Coded Graphic Character Sets - Latin/Cyrillic Alphabet 3rd edition (December 1999)
  • Standard ECMA-114 : 8-Bit Single-Byte Coded Graphic Character Sets - Latin/Arabic Alphabet 2nd edition (December 2000)
  • Standard ECMA-118 : 8-Bit Single-Byte Coded Graphic Character Sets - Latin/Greek Alphabet (December 1986)
  • Standard ECMA-121 : 8-Bit Single-Byte Coded Graphic Character Sets - Latin/Hebrew Alphabet 2nd edition (December 2000)
  • Standard ECMA-128 : 8-Bit Single-Byte Coded Graphic Character Sets - Latin Alphabet No. 5 2nd edition (December 1999)
  • Standard ECMA-144 : 8-Bit Single-Byte Coded Character Sets - Latin Alphabet No. 6 3rd edition (December 2000)

• ISO/IEC 8859-1 to Unicode mapping tables as plain text files are at the Unicode FTP site.

• Informal descriptions and code charts for most ISO 8859 standards are available in ISO 8859 Alphabet Soup (Mirror)