International
Tables for
Crystallography
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. 20-21

Section 2.2.2. Terminology

S. R. Halla* and J. D. Westbrookb

2.2.2. Terminology

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A summary of the basic terminology used throughout this chapter and the volume follows. A more extensive description of this terminology is given as formal specifications in Section 2.2.7.1.2[link].

(i) A CIF is a file conforming to the specification presented in this chapter. The term includes both data files containing information on a structural experiment or its results (or similar scientific content) and the dictionary files that provide descriptions of the data identifiers used in such data files.

(ii) A data name or tag is an identifier (a string of characters beginning with an underscore character) of the content of an associated data value.

(iii) A data value is a string of characters representing a particular item of information. It may represent a single numerical value; a letter, word or phrase; extended discursive text; or in principle any coherent unit of data such as an image, audio clip or virtual-reality object.

(iv) A data item is a specific piece of information defined by a data name and its associated data value.

(v) A data block is the highest-level component of a CIF, containing data items or (in the case of dictionary files only) save frames. A data block is identified by a data-block header, which is an isolated character string (that is, bounded by white space and not forming part of a data value) beginning with the case-insensitive reserved characters data_. A block code is the variable part of a data-block header, e.g. the string foo in the header data_foo.

(vi) A looped list of data is a set of data items represented as a table or matrix of values. The data names are assembled immediately following the word loop_, each separated by white space, and the associated data values are then listed in strict rotation. The table of values is assembled in row-major order; that is, the first occurrence of each of the data items is assembled in sequence, then the second occurrence of each item, and so forth. In a CIF, looped lists may not be nested.








































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