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, p. 34

Section Subtyping

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

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(18) The base data types detailed in the previous section are very general and need to be refined for practical application. Refinement of types is to some extent application-dependent, and different subtypes are supported for data items defined by DDL1 and DDL2 dictionary files. The following notes indicate some considerations, but the relevant dictionary files and documentation should be consulted in each case.

(19) DDL1 dictionaries. Values of type `numb' may include a standard uncertainty in the final digit(s) of the number where the associated item definition includes the attribute [Scheme scheme30] (or _type_conditions su, a synonym introduced to DDL1 in 2005). For example, a value of 34.5(12) means 34.5 with a standard uncertainty of 1.2; it may also be expressed in scientific notation as 3.45E1(12).

(20) DDL2 dictionaries. DDL2 provides a number of tags that may be used in a dictionary file to specify subtypes for data items defined by that dictionary alone. Examples of the subtypes specified for the macromolecular CIF dictionary are:

code identifying code strings or single words
ucode identifying code strings or single words (case-insensitive)
uchar1 single-character codes (case-insensitive)
uchar3 three-character codes (case-insensitive)
line character strings forming a single line of text
uline character strings forming a single line of text (case-insensitive)
text multi-line text
int integers
float floating-point real numbers
yyyy-mm-dd dates
symop symmetry operations
any any type permitted

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