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. 3.1, pp. 85-86

Section Identification of dictionaries relevant to a data file

B. McMahona*

aInternational Union of Crystallography, 5 Abbey Square, Chester CH1 2HU, England
Correspondence e-mail: Identification of dictionaries relevant to a data file

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A CIF data file should declare within each of its data blocks the names, version numbers and, where appropriate, locations of the global and local dictionaries that contain definitions of the data names used in that block. For DDL1 dictionaries, the relevant identifiers are the items _audit_conform_dict_name, _audit_conform_dict_version and _audit_conform_dict_location, defined in the core dictionary. DDL2 dictionaries are identified by the equivalent items _audit_conform.dict_name, *.dict_version and *.dict_location. For convenience, the DDL1 versions will be used in the following discussion.

The values of the items _audit_conform_dict_name and _audit_conform_dict_version are character strings that match the values of the _dictionary_name and _dictionary_version identifiers in the dictionary that defines the relevant data names. Validation against the latest version of a dictionary should always be sufficient, since every effort is made to ensure that a dictionary evolves only by extension, not by revising or removing parts of previous versions of the dictionary. Nevertheless, including _audit_conform_dict_version is encouraged: it can be useful to confirm which version of the dictionary the CIF was initially validated against.

The data item _audit_conform_dict_location may be used to specify a file name or uniform resource locator (URL). However, a file name on a single computer or network will be of use only to an application with the same view of the local file system, and so is not portable. A URL may be a better indicator of the location of a dictionary file on the Internet, but can go out of date as server names, addresses and file-system organization change over time. The preferred method for locating a dictionary file is to make use of a dynamic register, as described in Section[link]. Nevertheless, _audit_conform_dict_location remains a valid data item that may be of legitimate use, particularly in managing local applications.

The following example demonstrates a statement of dictionary conformance in a data file describing a powder diffraction experiment with some additional local data items: [Scheme scheme19] It is clear that the location specified for the local dictionary is only meaningful for applications running on the same computer or network, and therefore the ability to validate against this local dictionary is not portable. On the other hand, it may be that the local data names used by the authors of this CIF are not intended to have meaning outside their own laboratory.

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