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

International Tables for Crystallography (2006). Vol. G, ch. 2.2, pp. 33-34

Section Data typing

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

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(15) Four base data types are supported in CIF. These are:

(i) numb: a value interpretable as a decimal base number and supplied as an integer, a floating-point number or in scientific notation;

(ii) char: a value to be interpreted as character or text data (where the value contains white-space characters, it must be quoted);

(iii) uchar: a value to be interpreted as character or text data but in a case-insensitive manner (i.e. the values FOO and foo are to be taken as identical);

(iv) null: a special data type associated with items for which no definite value may be stored in computer memory. It is the type associated with the special character literal values ? (query mark) and . (full point), which may appear as values for any data item within a data file (see Section[link] below). It is also the type assigned to items defined in dictionary files that may not occur in data files.

(16) Comment: Many applications distinguish between multi-line text fields and character-string values that fit within a single line of text. While this is a convenient practical distinction for coding purposes, formally both manifestations should be regarded as having the same base type, which might be `char' or `uchar'. Applications are at liberty to choose whether to define specific multi-line text subtypes, and whether to permit casting between subtypes of a base type. The examples of character-string delimiters in Section[link](20) are predicated on an approach that handles all subtypes of character or text data equivalently.

(17) Where the attributes of a data value are not available in a dictionary listing, it may be assumed that a character string interpretable as a number should be taken to represent an item of type `numb'. However, an explicit dictionary declaration of type will override such an assumption.

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