[Unicode]  Unicode Character Database

Derived Character Properties

Revision 3.1.1
Authors Mark Davis
Date 2001-08-08
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This document describes the format and content of the main derived data files in the Unicode Character Database (UCD).


The file and the files described herein are part of the Unicode Character Database and governed by the UCD Terms of Use given below.

For general information on file formats and table formats, and the implications of normative vs informative properties, see UnicodeCharacterDatabase.html.

Warning: the information in this file does not completely describe the use and interpretation of Unicode character properties and behavior. It must be used in conjunction with the data in the other files in the UCD, and relies on the notation and definitions supplied in The Unicode Standard. All chapter references are to Version 3.1.0 of the standard.


This document describes a number of data files in the Unicode Character database. These are the Derived data files, containing information that can be completely derived from other data files, but is presented in a different format for ease of use.

The files themselves are informative, although they may contain normative properties. For more information, see UnicodeCharacterDatabase.html.

Derived Core Properties

The following are important derived properties of Unicode characters, and are contained in DerivedCoreProperties.txt.

Property Value N/I Definition and Generation
Math I Characters with the Math property. For more information, see Chapter 4, Character Properties.
Generated from: Sm + Other_Math
Alphabetic I Characters with the Alphabetic property. For more information, see Chapter 4, Character Properties.
Generated from: Lu+Ll+Lt+Lm+Lo+ Other_Alphabetic
Lowercase I Characters with the Lowercase property. For more information, see Chapter 4, Character Properties and UTR #21: Case Mappings.
Generated from: Ll + Other_Lowercase
Uppercase I Characters with the Uppercase property. For more information, see Chapter 4, Character Properties and UTR #21: Case Mappings.
Generated from: Lu + Other_Uppercase
ID_Start I Characters that can start an identifier.
Generated from Lu+Ll+Lt+Lm+Lo+Nl
ID_Continue I Characters that can continue an identifier. See Cf Note.
Generated from: ID_Start + Mn+Mc+Nd+Pc
XID_Start I Same as ID_Start, except for modifications to allow closure under normalization forms NFKC and NFKD.
Generated from: ID_Start; see Closure Note
XID_Continue I Same as ID_Continue, except for modifications to allow closure under normalization forms NFKC and NFKD. See Closure Note and Cf Note.
Generated from: ID_Continue; see Closure Note

Closure Note: XID_Start and XID_Continue are defined by adding or removing certain special characters as per UAX #15, Annex 7. They do not remove the non-NFKD nor the non_NFKC characters; if that is desired it needs to be a separate filter. They merely ensure that:

if isIdentifer(string)
then isIdentifier(NFKC(string))
and isIdentifier(NFKD(string))

Cf Note: The general category Cf characters are not included in ID_Continue nor in XID_Continue; they should continue identifiers, but be filtered out of the result.

For more information on identifiers, see Chapter 5, Implementation Guidelines, and UAX #15, Annex 7.

Derived Extracted Properties

The following files contain other properties of the UCD that are simply separated out, and listed in range format. These files are provided purely as a reformatting of existing data, with a certain exceptions listed below.

".txt" Files N/I Definition and Generation
DerivedGeneralCategory N From UnicodeData.txt, field 2
DerivedCombiningClass N From UnicodeData.txt, field 3
DerivedBidiClass N From UnicodeData.txt, field 4
DerivedDecompositionType * From the <tag> in UnicodeData.txt, field 5. For characters with canonical decomposition mappings (no tag), the value "canonical" is used.

* The value "canonical" is normative; the others are informative.

DerivedNumericType N The property value is is based on the contents of UnicodeData.txt, fields 6 through 8:
property value non-empty fields
decimal 6, 7, & 8
digit 7 & 8
numeric 8
DerivedNumericValues N From UnicodeData.txt, field 8
DerivedBinaryProperties N From UnicodeData.txt, field 9. See Bidi Note.
DerivedEastAsianWidth I From EastAsianWidth.txt, field 1
DerivedLineBreak * From LineBreak.txt, field 1.

* Some values are normative; some are informative. See UTR #11: Line Break Property for more information.

DerivedJoiningType N From ArabicShaping.txt, field 1
DerivedJoiningGroup N From ArabicShaping.txt, field 2

Bidi Note: The BidiMirrored property and the BidiMirroring property are different. The former is a normative property that indicates whether characters are mirrored in a right-to-left context in the Unicode Bidirectional Algorithm. The latter is an informative mapping of BidiMirrored characters, where possible, to characters that normally have the corresponding mirrored glyph.

Derived Normalization Properties

The properties in DerivedNormalizationProperties.txt are useful in dealing with normalization forms. In the following table, NF* refers to one of NFD, NFC, NFKC, or NFKD.

Property Value N/I Definition and Generation
FNC N Characters that require extra mappings for closure under Case Folding plus Normalization Form KC. Characters marked with this property have a third field with the mapping in it. Generated with the following:
b = NFKC(Fold(a));
c = NFKC(Fold(b));
if (c != b) add mapping from a to c
Comp_Ex N Characters that are excluded from composition: those explicitly in CompositionExclusions.txt, plus:
(3) Singleton Decompositions
(4) Non-Starter Decompositions
NF*_NO N Characters that cannot ever occur in NF*. See QuickCheck Note.
NF*_MAYBE N Characters that may occur in valid NF*, depending on the context. See QuickCheck Note.
NF*_Expands N Characters that expand to more than one character in the specified normalization form.

QuickCheck Note: A previous version of this data was in NormalizationQuickCheck.txt. For more information, see UAX #15 Annex 8.)

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