View source for CCSID

{{Short description|Identifier of a coded character set}}
A '''CCSID''' ('''coded character set identifier''') is a 16-bit number that represents a particular [[Character encoding|encoding]] of a specific [[Code page|code page]]. For example, [[Unicode]] is a code page that has several character encoding schemes (referred to as "transformation forms")—including [[UTF-8]], [[UTF-16]] and [[UTF-32]]—but which may or may not actually be accompanied by a CCSID number to indicate that this encoding is being used.

==Difference between a code page and a CCSID==
The terms '''code page''' and '''CCSID''' are often used interchangeably, even though they are not synonymous. A code page may be only part of what makes up a CCSID. The following definitions from IBM help to illustrate this point:

* A '''glyph''' is the actual physical pattern of pixels or ink that shows up on a display or printout.

* A '''character''' is a concept that covers all glyphs associated with a certain symbol. For instance, "F", "'''F'''", "''F''", "{{underline|F}}", "{{red|F}}", and "{{mono|F}}" are all different glyphs, but use the same character. The various modifiers (bold, italic, underline, color, and font) do not change the F's essential F-ness.

* A '''character set''' contains the characters necessary to allow a particular human to carry on a meaningful interaction with the computer. It does not specify how those characters are represented in a computer.<ref name="IBM Terminology: C">{{cite web |url=http://www-01.ibm.com/software/globalization/terminology/c.html |title=IBM Terminology—Terms C |publisher=[[Company:IBM|IBM]] |access-date=2013-01-25}}</ref> This level is the first one to separate characters into various alphabets (Latin, Arabic, Hebrew, Cyrillic, and so on) or ideographic groups (e.g., Chinese, Korean). It corresponds to a "character repertoire" in the Unicode encoding model.

* A '''code page''' represents a particular assignment of code point values to characters.{{r|IBM Terminology: C}} It corresponds to a "coded character set" in the Unicode encoding model. A '''code point''' for a character is the computer's internal representation of that character in a given code page.{{r|IBM Terminology: C}} Many characters are represented by different code points in different code pages. Certain character sets can be adequately represented with single-byte code pages (which have a maximum 256 code points, hence a maximum of 256 characters), but many require more than that. Examples include [[JIS X 0208]] and [[Unicode]].

* An '''encoding scheme''' is the byte format of a code page. It maps code point values to sequences of one or more byte values in a computer.<ref>{{cite web |url=https://www.ibm.com/downloads/cas/G01BQVRV |title=Character Data Representation Architecture |at=Appendix A. Encoding Schemes |publisher=[[Company:IBM|IBM]] |access-date=2019-06-29}}</ref> For example, [[UTF-8]] and [[UTF-16BE]] are two encodings of the same Unicode code page. (Varying only in how many bytes are needed to represent a particular Unicode character value, how it is contained within those bytes, and how the presence of Unicode information is indicated.) Meanwhile, in IBM's character data representation architecture (CDRA), this is typically represented with an ESID (encoding scheme identifier).<ref>{{cite web |url=https://www.ibm.com/downloads/cas/G01BQVRV |title=Character Data Representation Architecture |at=Chapter 3. CDRA Identifiers, section "Long-Form Identification" |publisher=[[Company:IBM|IBM]] |access-date=2019-06-29}}</ref> EUC and ISO-2022 are other examples of encoding schemes.

* A '''coded character set identifier''' ('''CCSID''') contains all of the information necessary to assign and preserve the meaning and rendering of characters through various stages of processing and interchange. This information always includes at least one code page, but may include multiple code pages of differing byte-lengths. The CCSID also has an associated encoding scheme that governs how various code points are to be handled. This mechanism allows a program to recognize bidirectional orientation, character shaping (mainly of Arabic characters), and other complex encoding information.

==Examples==
The following examples show how some CCSIDs are made up of other CCSIDs.

{| class="wikitable"
|+ CCSID 932<ref>{{cite web |url= http://www.ibm.com/software/globalization/ccsid/ccsid932.html |title= Japanese PC Data Mixed including 1880 UDC |publisher= IBM |work= Globalization |url-status= dead |archive-date= February 20, 2012 |archive-url= https://web.archive.org/web/20120220153419/http://www-01.ibm.com/software/globalization/ccsid/ccsid932.html |access-date= November 29, 2011 }}</ref>
|-
! Character set
! Code page
! CCSID
! Encoding scheme
|-
| 01122
| 00897
| 897
| {{abbr|SBCS|Single-byte character set}}
|-
| 00370
| 00301
| 301
| {{abbr|DBCS|Double-byte character set}}
|}

{| class="wikitable"
|+ CCSID 942<ref>{{cite web |url= http://www.ibm.com/software/globalization/ccsid/ccsid942.html |title= Japanese PC Data Mixed including 1880 UDC, Extended SBCS |publisher= IBM |work= Globalization |url-status= dead |archive-date= December 1, 2014 |archive-url= https://web.archive.org/web/20141201234629/http://www-01.ibm.com/software/globalization/ccsid/ccsid942.html |access-date= November 29, 2011 }}</ref>
|-
! Character set
! Code page
! CCSID
! Encoding scheme
|-
| 01172
| 01041
| 1041
| SBCS
|-
| 00370
| 00301
| 301
| DBCS
|}

{| class="wikitable"
|+ CCSID 5028<ref>{{cite web |url= http://www.ibm.com/software/globalization/ccsid/ccsid5028.html |title= Japanese PC Data Mixed including 1880 UDC (Katakana - PC common set for SBCS) |publisher= IBM |work= Globalization |url-status= dead |archive-date= November 29, 2014 |archive-url= https://web.archive.org/web/20141129225910/http://www-01.ibm.com/software/globalization/ccsid/ccsid5028.html |access-date= November 29, 2011 }}</ref>
|-
! Character set
! Code page
! CCSID
! Encoding scheme
|-
| 01170
| 00897
| 4993
| SBCS
|-
| 00370
| 00301
| 301
| DBCS
|}

All three of these variant Shift-JIS CCSIDs are multi-byte character sets (MBCS): the single-byte character set (SBCS) portion of each CCSID is different. The [[Double-byte character set|double-byte character set]] (DBCS) portion is the same across each CCSID. CCSID 5028 uses an updated code page 897 called CCSID 4993. CCSID 932 uses the original code page 897, which is CCSID 897. CCSID 942 uses a different SBCS from the other two CCSIDs, which is 1041.

Also notice how CCSID 5028 and 4993 are different by 4096 (1000 in hexadecimal) from the predecessor CCSID with the same code page identifier. This is a common way that CDRA denotes an upgraded CCSID.

There are a few reasons for this complexity:

* Many of the CCSIDs are used in IBM databases, like [[Software:IBM Db2|IBM Db2]], where a database field only supports an SBCS, DBCS or MBCS string. CCSIDs allow programs to differentiate between which one is being used.
* When characters are added or replaced, like the Euro currency sign introduction, one can know whether the stored strings support or do not support those character additions because a different CCSID is being used. This versioning is important for the integrity of the data.
* It enables reuse of resources among similar CCSIDs.<ref>{{Cite web|url=http://www.ibm.com/software/globalization/cdra/chapter7.html|title=Us-en_software_HP|date=9 November 2020}}</ref>

==References==
{{Reflist}}

==External links==
* [https://web.archive.org/web/20160305141156/http://www-01.ibm.com/software/globalization/cdra/glossary.html IBM CDRA (character data representation architecture) glossary of terms]
* [https://web.archive.org/web/20161110150629/http://www-01.ibm.com/software/globalization/terminology/ IBM globalization terminology]
* [https://www.ibm.com/downloads/cas/G01BQVRV Complete description of IBM CDRA]. (This includes a more detailed description of the architecture surrounding CCSIDs.)
* [https://web.archive.org/web/20160304082631/http://www-01.ibm.com/software/globalization/g11n-res.html IBM's complete list of CCSIDs and other various related identifiers]
* [https://web.archive.org/web/20150406044931/http://www-03.ibm.com/systems/i/software/globalization/ccsid_list.html List of CCSIDs supported on the IBM System i computer]

{{character encoding}}

[[Category:Character encoding]]

{{Sourceattribution|CCSID}}