International
Tables for
Crystallography
Volume G
Definition and exchange of crystallographic data
Edited by S. R. Hall and B. McMahon

© International Union of Crystallography 2006
International Tables for Crystallography (2006). Vol. G. ch. 2.2, pp. 28-29

Table 2.2.7.1 

S. R. Hall,a* N. Spadaccini,c I. D. Brown,d H. J. Bernstein,e J. D. Westbrookb and B. McMahonf

Table 2.2.7.1 | top | pdf |
A formal grammar for CIF

(a) Basic structure of a CIF.

Syntactic unit Syntax Case sensitive?
<CIF> <Comments>? <WhiteSpace>? { <DataBlock> { <WhiteSpace> <DataBlock> }* { <WhiteSpace> }? }? yes
<DataBlock> <DataBlockHeading> {<WhiteSpace> { <DataItems> | <SaveFrame>} }* yes
<DataBlockHeading> <DATA_> { <NonBlankChar> }+ no
<SaveFrame> <SaveFrameHeading> { <WhiteSpace> <DataItems> }+ <WhiteSpace> <SAVE_> yes
<SaveFrameHeading> <SAVE_> { <NonBlankChar> }+ no
<DataItems> <Tag> <WhiteSpace> <Value> | <LoopHeader> <LoopBody> yes
<LoopHeader> <LOOP_> {<WhiteSpace> <Tag>}+ no
<LoopBody> <Value> { <WhiteSpace> <Value> }* yes

(b) Reserved words.

Syntactic unit Syntax Case sensitive?
<DATA_> {'D'|'d'} {'A'|'a'} {'T'|'t'} {'A'|'a'} '_' no
<LOOP_> {'L'|'l'} {'O'|'o'} {'O'|'o'} {'P'|'p'} '_' no
<GLOBAL_> {'G'|'g'} {'L'|'l'} {'O'|'o'} {'B'|'b'} {'A'|'a'} {'L'|'l'} '_' no
<SAVE_> {'S'|'s'} {'A'|'a'} {'V'|'v'} {'E'|'e'} '_' no
<STOP_> {'S'|'s'} {'T'|'t'} {'O'|'o'} {'P'|'p'} '_' no

(c) Tags and values.

Syntactic unit Syntax Case sensitive?
<Tag> '_'{ <NonBlankChar>}+ no
<Value> { '.' | '?' | <Numeric> | <CharString> | <TextField> } yes

(d) Numeric values.

Syntactic unit Syntax Case sensitive?
<Numeric> { <Number> | <Number> '(' <UnsignedInteger> ')' } no
<Number> {<Integer> | <Float> } no
<Integer> {{ '+' | '-' }? <UnsignedInteger> no
<Float> { <Integer><Exponent> | { {'+'|'-'} ? { {<Digit>} * '.' <UnsignedInteger> } | { <Digit>} + '.' } } {<Exponent>} ? } } no
<Exponent> { {'e' | 'E' } | {'e' | 'E' } { '+' | '-' } } <UnsignedInteger> no
<UnsignedInteger> { <Digit> }+ no
<Digit> { '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' } no

(e) Character strings and text fields.

Syntactic unit Syntax Case sensitive?
<CharString> <UnquotedString> | <SingleQuotedString> | <DoubleQuotedString> yes
<eol><UnquotedString> <eol><OrdinaryChar> {<NonBlankChar>}* yes
<noteol><UnquotedString> <noteol>{<OrdinaryChar>|';'} {<NonBlankChar>}* yes
<SingleQuotedString><WhiteSpace> <single_quote>{<AnyPrintChar>}* <single_quote> <WhiteSpace> yes
<DoubleQuotedString><WhiteSpace> <double_quote> {<AnyPrintChar>}* <double_quote> <WhiteSpace> yes
<TextField> { <SemiColonTextField> } yes
<eol><SemiColonTextField> <eol>';' { {<AnyPrintChar>}* <eol> {{<TextLeadChar> {<AnyPrintChar>}*}? <eol>}* } ';' yes

(f) White space and comments.

Syntactic unit Syntax Case sensitive?
<WhiteSpace> { <SP>|<HT>|<eol>|<TokenizedComments>}+ yes
<Comments> { '#' {<AnyPrintChar>}* <eol>}+ yes
<TokenizedComments> { <SP>|<HT>|<eol>|}+ <Comments> yes

(g) Character sets.

Syntactic unit Syntax Case sensitive?
<OrdinaryChar> ' { '!'|'%'|'&'|'('|')'|'*'|'+'|','|'-'|'.'|'/'|'0'|'1'|'2'|'3'|'4'|'5'| '6'|'7'|'8'|'9'|':'|'<'|'='|'>'|'?'|'@'|'A'|'B'|'C'|'D'|'E'|'F'|'G'|'H'| 'I'|'J'|'K'|'L'|'M'|'N'|'O'|'P'|'Q'|'R'|'S'|'T'|'U'|'V'|'W'|'X'|'Y'|'Z'| '\'|'^'|'`'|'a'|'b'|'c'|'d'|'e'|'f'|'g'|'h'|'i'|'j'|'k'|'l'|'m'|'n'|'o'| 'p'|'q'|'r'|'s'|'t'|'u'|'v'|'w'|'x'|'y'|'z'|'{'|'|'|'}'|'~' } yes
<NonBlankChar> <OrdinaryChar>|<double_quote>|'#'|'$'|<single_quote>|'_' |';'|'['|']' yes
<TextLeadChar> <OrdinaryChar>|<double_quote>|'#'|'$'|<single_quote>|'_'|<SP>|<HT>|'['|']' yes
<AnyPrintChar> <OrdinaryChar>|<double_quote>|'#'|'$'|<single_quote>|'_'|<SP>|<HT>|';'|'['|']' yes